Radio reception system

ABSTRACT

When once determined to be free of any demodulation error by an interference removing unit provided user by user, a replica signal calculated by the interference removing unit is subtracted from an input signal vector, and a calculated user signal is output as it is as a final user signal. When it is determined by the interference removing unit that there is a demodulation error, the user signal is again calculated by the interference removing unit of an interference canceller of a next stage. As subtraction of the replica signal corresponding to the user signal having a demodulation error from the input signal vector is inhibited, precision of the interference wave removal can be improved.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.10/089,076 filed on Apr. 9, 2002 which is a national stage applicationof PCT/JP00/07041 filed Oct. 10, 2000, which claims priority of JP11-290093 (P) filed Oct. 12, 1999, which are hereby incorporated byreference in their entirety. Priority under 35 U.S.C. §§120 and 121 ishereby claimed for benefit of the filing date of U.S. patent applicationSer. No. 10/089,076.

TECHNICAL FIELD

The present invention relates to a radio reception system, and morespecifically to a radio reception system in accordance with acommunication method such as PDMA (Path Division Multiple Access), CDMA(Code Division Multiple Access) and the like, which is capable ofremoving, from a received signal, an interfering signal component fromother user.

BACKGROUND ART

Recently, various methods of transmission channel allocation have beenproposed to realize effective use of frequency, in mobile communicationsystems such as mobile telephones, of which some have been practicallyimplemented.

FIG. 22 shows an arrangement of channels in various communicationsystems including FDMA (Frequency Division Multiple Access), TDMA (TimeDivision Multiple Access) and PDMA. Referring to FIG. 22, FDMA, TDMA andPDMA will be briefly described.

FIG. 22( a) represents channel arrangement of FDMA, in which analogsignals of users 1 to 4 are subjected to frequency division andtransmitted over radio waves of different frequencies f1 to f4, and thesignals of respective users 1 to 4 are separated by frequency filters.

FIG. 22( b) represents a channel arrangement of TDMA, in which digitizedsignals of respective users are transmitted over the radio waves havingdifferent frequencies f1 to f4 and time-divided time slot by time slot(time slot: a prescribed time period), and the signals of respectiveusers 1 to 8 are separated by the frequency filters andtime-synchronization between a base station and mobile terminals ofrespective users.

Recently, PDMA method has been proposed to improve efficiency of use ofradio frequency, as mobile telephones have come to be widely used. Inthe PDMA method, one time slot of one frequency is spatially divided toenable transmission of data of a plurality of users, as shown in FIG.22( c). In the PDMA, signals of respective users are separated by thefrequency filters, the time synchronization between the base station andthe mobile terminals of respective users, and a signal extractingapparatus such as an adaptive array.

FIG. 23 represents a reception system of a conventional PDMA basestation. In this example, in order to identify users 1 and 2, fourantennas 3 to 6 are provided, outputs of respective antennas are appliedto a frequency converting circuit 7, subjected to frequency conversionby corresponding local oscillation signal Lo, respectively, converted todigital signals by an A/D converter 8 and applied to a digital signalprocessor (DSP) 10.

DSP 10 includes adaptive arrays 11, 12, a reception signal vectorcalculator 13, a memory 14, a correlation value calculator 15 and achannel allocating apparatus 16. Adaptive arrays 11 and 12 extract, fromreception signals output from A/D converter 8, only those signals from aspecific user. Each adaptive array extracts a user signal designated bychannel allocating apparatus 16, which will be described later, inaccordance with a weight vector calculating method such as a methodutilizing a preamble included in a time slot or a method utilizing anature that an envelop of a modulation signal becomes constant, forexample.

Reception signal vector calculator 13 receives as inputs the receptionsignals from A/D converter 8 and output signals from adaptive arrays 11,12, calculates reception signal vectors corresponding to every user, andstores the results in memory 14. Channel allocating apparatus 16designates two users for the memory 14 and the correlation valuecalculator 15. Correlation value calculator 15 calculates, among thereception signal vectors stored in memory 14, correlation value betweenreception signal vectors of the designated two users. Channel allocatingapparatus 16 receives the calculated correlation value between thereception signal vectors of the two users. When the correlation value isnot larger than a prescribed value, the two users are subjected to pathdivision multiple connection to a time slot of the same time.

Adaptive arrays 11 and 12 shown in FIG. 23 extract signals ofcorresponding users 1 and 2, respectively. When a user 3 transmits asignal from the same direction as user 1, in addition to users 1 and 2,it follows that the signals from users 1 and 3 are mixed and output fromadaptive array 11. The conventional adaptive array 11, however, cannotseparate the signals of users 1 and 3, and hence, it has been impossibleto extract the signal of user 1 only.

Therefore, an object of the present invention is to provide a radioreception system that can improve communication quality, by cancelingunnecessary user signals using an interference canceller.

DISCLOSURE OF THE INVENTION

The present invention provides a radio reception system capable ofreceiving signals from a plurality of users using a plurality ofantennas, including: signal processing means for performing a prescribedsignal processing on the signals received by the plurality of antennas;a plurality of first signal extracting means for extracting signalcomponents corresponding to the plurality of users, respectively, basedon a signal output from the signal processing means; a plurality offirst estimating means for estimating parameter information related torelation between the signal components extracted by the first signalextracting means and the signal output from the signal processing means;a plurality of first error determining means for determining whether thesignal components corresponding to the plurality of users extracted bythe first signal extracting means include a demodulation error or not,respectively; and first operating means for subtracting, from the signaloutput from the signal processing means, the extracted signal componentdetermined by the first error determining means not to include anydemodulation error, in consideration of corresponding parameterinformation.

Preferably, the radio reception system further includes a plurality ofsecond signal extracting means for extracting, based on the signaloutput from the first operating means, signal components correspondingto users determined by the first error determining means to include ademodulation error, respectively; a plurality of second estimating meansfor estimating parameter information related to relation between thesignal components extracted by the second signal extracting means andthe signal output from the first operating means; and a plurality ofsecond error determining means for determining whether the signalcomponents extracted by the second signal extracting means include ademodulation error or not, respectively.

More preferably, the radio reception system further includes secondoperating means for subtracting, from the signal output from the signalprocessing means, the signal component extracted by the first and secondsignal extracting means determined by the first and second errordetermining means not to include any demodulation error, inconsideration of corresponding parameter information.

More preferably, the radio reception system further includes thirdoperating means subtracting, from the signal output from the firstoperating means, the signal component extracted by the second signalextracting means determined by the second error determining means not toinclude any demodulation error, in consideration of correspondingparameter information.

According to another aspect, the present invention provides a radioreception system capable of receiving signals from a plurality of usersusing a plurality of antennas, including: signal processing means forperforming a prescribed signal processing on the signals received by theplurality of antennas; a plurality of first signal extracting means forextracting signal components corresponding to the plurality of users,respectively, based on a signal output from the signal processing means;a plurality of first estimating means for estimating parameterinformation related to relation between the signal components extractedby the first signal extracting means and the signal output from thesignal processing means based on a correlation value between signalcomponent of the corresponding user and signal component of anotheruser; a plurality of first error determination means for determiningwhether the signal components corresponding to the plurality of usersextracted by the first signal extracting means include a demodulationerror or not, respectively; and first operating means for subtracting,from the signal output from the signal processing means, the extractedsignal component determined by the first error determining means not toinclude any demodulation error, in consideration of correspondingparameter information.

Preferably, the radio reception system further includes a plurality ofsecond signal extracting means for extracting, based on the signaloutput from the first operating means, signal components correspondingto users determined by the first error determining means to include ademodulation error, respectively; a plurality of second estimating meansfor estimating parameter information related to relation between thesignal components extracted by the second signal extracting means andthe signal output from the first operating means based on a correlationvalue between signal component of the corresponding user and signalcomponent of another user; and plurality of second error determiningmeans for determining whether the signal components extracted by thesecond signal extracting means include a demodulation error or not,respectively.

More preferably, the radio reception system further includes secondoperating means for subtracting, from the signal output from the signalprocessing means, the signal component extracted by the first and secondsignal extracting means determined by the first and second errordetermining means not to include any demodulation error, inconsideration of corresponding parameter information.

More preferably, the radio reception system further includes thirdoperating means subtracting, from the signal output from the firstoperating means, the signal component extracted by the second signalextracting means determined by the second error determining means not toinclude any demodulation error, in consideration of correspondingparameter information.

More preferably, the plurality of first estimating means estimate theparameter information by calculating the correlation value, independentfrom result of determination by the plurality of first errordetermination means.

More preferably, the plurality of first estimating means estimate theparameter information by calculating the correlation value using signalcomponents of the users determined not to include any demodulationerror, based on the result of determination by the plurality of firsterror determining means.

More preferably, the plurality of second estimating means estimate theparameter information by calculating the correlation value, independentfrom result of determination by the plurality of second errordetermination means.

More preferably, the plurality of second estimating means estimate theparameter information by calculating the correlation value using signalcomponents of the users determined not to include any demodulationerror, based on the result of determination by the plurality of seconderror determining means.

According to a still further aspect, the present invention provides aradio reception system capable of receiving signals from a plurality ofusers using a plurality of antennas, including: signal processing meansfor performing a prescribed signal processing on the signals received bythe plurality of antennas; and one stage of interference cancellers,including a plurality of stages of interference removing unitscorresponding to the plurality of users; wherein each stage of theinterference removing unit includes signal extracting means forextracting signal component corresponding to a specific user, differentstage by stage, among the plurality of users based on an input signal,estimating means for estimating parameter information related torelation between the signal component extracted by the signal extractingmeans and the signal input to the signal extracting means, operatingmeans for removing the signal component corresponding to the specificuser, from the signal input to the signal extracting means inconsideration of the parameter information, and error determining meansfor determining whether the signal component corresponding to thespecific user includes a demodulation error or not, and when determinedto include the demodulation error, disabling removal of the signalcomponent corresponding to the specific user by the operating means; andthe plurality of stages of interference removing units are connectedsuch that the signal output from the signal processing means is input toinputs of the operating means and the signal extracting means of thefirst stage of the interference removing units, and an output of theoperating means of a former stage interference removing unit of adjacenttwo interference removing units is applied to inputs of the signalextracting means and the operating means of a latter stage interferenceremoving unit.

Preferably, the radio reception system further includes a next stage ofinterference cancellers receiving an output of the operating means of alast stage interference removing unit of the one stage of interferencecancellers; wherein the next stage interference canceller includes aplurality of stages of interference removing units corresponding to theplurality of users; each stage of the interference removing unitsincludes signal extracting means for extracting and outputting signalcomponent corresponding to a specific user, different stage by stage,among the plurality of users, based on an input signal, estimating meansfor estimating parameter information related to relation between thesignal component extracted by the signal extracting means and the signalinput to the signal extracting means, operating means for removing thesignal component corresponding to the specific user from the signalsinput to the signal extracting means, in consideration of the parameterinformation, and error determining means for determining whether thesignal component corresponding to the specific user includes ademodulation error or not and, when determined to include an error,disabling removal of the signal component corresponding to the specificuser by the operating means; the interference removing unit of the nextstage interference canceller corresponding to a user determined not toinclude any demodulation error by the interference canceller of thefirst stage provides an output of the interference removing unit of thepreceding stage as it is to the interference removing unit of thesucceeding stage; and in the interference removing unit of the nextstage interference canceller corresponding to the user determined toinclude a demodulation error by the first stage interference canceller,an output of the interference removing unit of the preceding stage isapplied to inputs of the signal extracting means and the operatingmeans, and an output of the operating means is output to theinterference removing unit of the succeeding stage.

According to a still further aspect, the present invention includes aradio reception system capable of receiving signals from a plurality ofusers using a plurality of antennas, including: signal processing meansfor performing a prescribed signal processing on the signals received bythe plurality of antennas; and one stage of interference cancellers; theone stage of interference cancellers includes a plurality of stages ofinterference removing units corresponding to the plurality of users;each stage of the interference removing units includes signal extractingmeans for extracting and outputting signal component corresponding to aspecific user, different stage by stage, among the plurality of users,based on an input signal, estimating means for estimating, based on acorrelation value between signal component of the specific user andsignal component of another user, parameter information related torelation between the signal component extracted by the signal extractingmeans and the signal output from the signal processing means, errordetermining means for determining whether the signal componentcorresponding to the specific user includes a demodulation error or not,and operating means for removing the signal component corresponding to auser determined not to include a demodulation error from the signaloutput from the signal processing means, in consideration of theparameter information; and the plurality of stages of interferenceremoving units are connected such that the signal output from the signalprocessing means is input to inputs of the operating means and thesignal extracting means of the first stage of the interference removingunits, and an output of the operating means of a former interferenceremoving unit of adjacent two interference removing units is applied toan input of the signal extracting means of a latter stage interferenceremoving unit.

Preferably, the radio reception system further includes a next stage ofinterference cancellers receiving an output of the operating means ofthe interference removing unit of the last stage of the one stage ofinterference cancellers; wherein the next stage interference cancellerincludes a plurality of stages of interference removing unitscorresponding to the plurality of users; each stage of the interferenceremoving unit includes signal extracting means for extracting andoutputting signal component corresponding to a specific user, differentstage by stage, among the plurality of users based on an input signal,estimating means for estimating, based on a correlation value betweensignal component of the specific user and signal component of anotheruser, parameter information related to relation between the signalcomponent extracted by the signal extracting means and the signal outputfrom the signal processing means, error determining means fordetermining whether or not the signal component corresponding to thespecific user includes a demodulation error, and operating means forremoving the signal component corresponding to the user determined notto include any demodulation error from the signal output from the signalprocessing means, in consideration of the parameter information; theinterference removing unit of the next stage interference cancellercorresponding to the user determined not to include any demodulationerror by the first stage interference canceller outputs an output of theinterference removing unit of the preceding stage as it is to aninterference removing unit of the succeeding stage; and in theinterference removing unit of the next stage interference cancellercorresponding to the user determined to include a demodulation error bythe first stage interference canceller, an output of the interferenceremoving unit of the preceding stage is applied to an input of thesignal extracting means, and an output of the operating means is outputto the interference removing unit of the succeeding stage.

More preferably, the estimating means calculates correlation valuebetween the signal component of the specific user and signal componentof another user independent from result of determination by the errordetermining means, and estimates the parameter information based on thecalculated correlation value.

More preferably, the estimating means calculates the correlation valueusing only the signal components of the users determined not to includeany demodulation error based on the result of determination by the errordetermining means, and estimates the parameter information based on thecalculated correlation value.

More preferably, the signal extracting means is an adaptive arrayspatially separating and extracting signal component corresponding to aspecific user.

More preferably, the signal extracting means includes an adaptive arrayspatially separating and extracting signal component corresponding to aspecific user, a demodulator demodulating an output of the adaptivearray, and a re-modulator re-modulating an output of the demodulator.

More preferably, the signals from the plurality of users are signalstransmitted in accordance with PDMA communication method.

More preferably, the signals from the plurality of users are signalstransmitted in accordance with CDMA communication method.

More preferably, the signals transmitted in accordance with the CDMAcommunication method are spread by predetermined spreading codes inadvance on a transmitting side, and the radio reception system furtherincludes inverse spreading means for inverse spreading signals outputfrom the signal processing means by corresponding spreading codes inaccordance with CDMA communication method and applying the results tothe signal extracting means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a reception system of a PDMA base station,as a basic concept of the present invention.

FIG. 2 is a block diagram representing a configuration of the operatingapparatus shown in FIG. 1.

FIG. 3 is a block diagram of the reception system of the PDMA basestation in accordance with a first embodiment of the present invention.

FIG. 4 is a block diagram representing a configuration of aninterference removing unit shown in FIG. 3.

FIG. 5 is a block diagram representing a configuration of the operatingapparatus shown in FIG. 3.

FIG. 6 is a block diagram of the reception system of the PDMA basestation in accordance with a second embodiment of the present invention.

FIG. 7 is a block diagram representing a configuration of the operatingapparatus shown in FIG. 6.

FIG. 8 is a block diagram of the reception system of the PDMA basestation in accordance with a third embodiment of the present invention.

FIG. 9 is a block diagram representing a configuration of theinterference removing unit shown in FIG. 8.

FIG. 10 is a block diagram of the reception system for the PDMA basestation in accordance with a fourth embodiment of the present invention.

FIG. 11 is a block diagram of the reception system for the PDMA basestation in accordance with a fifth embodiment of the present invention.

FIG. 12 is a block diagram of the reception system for the PDMA basestation in accordance with a sixth embodiment of the present invention.

FIG. 13 is a block diagram of the reception system for the PDMA basestation in accordance with a seventh embodiment of the presentinvention.

FIG. 14 is a block diagram of the reception system for the PDMA basestation in accordance with the eighth and ninth embodiments of thepresent invention.

FIG. 15 is a block diagram representing a configuration of theinterference removing unit of the reception system for the PDMA basestation in accordance with the eighth embodiment of the presentinvention.

FIG. 16 is a block diagram representing a configuration of theinterference removing unit of the reception system for the PDMA basestation in accordance with the ninth embodiment of the presentinvention.

FIG. 17 is a block diagram of the reception system for the CDMA basestation in accordance with a tenth embodiment of the present invention.

FIG. 18 is a block diagram representing a configuration of theinterference removing unit shown in FIG. 17.

FIG. 19 is a block diagram representing a configuration of the operatingapparatus shown in FIG. 17.

FIG. 20 is a block diagram representing a configuration of theinterference removing unit of the reception system for the CDMA basestation in accordance with an eleventh embodiment of the presentinvention.

FIG. 21 is a block diagram representing a configuration of an adaptivearray.

FIG. 22 shows channel arrangements of user signals in accordance withcommunication methods of FDMA, TDMA and PDMA, respectively.

FIG. 23 is a block diagram representing the conventional receptionsystem for the PDMA base station.

BEST MODES FOR CARRYING OUT THE INVENTION

FIG. 1 is a block diagram representing a reception system for the PDMAbase station proposed as a multistage interference canceller as a basicconcept of the present invention. In the proposed reception system asthe basic concept of the present invention, signals S₁(t), . . . ,S_(k)(t), . . . , S_(m)(t) from m (m is an integer not smaller than 2)users 1, . . . , k, . . . , m transmitted at the same time are mutuallyseparated and taken out in parallel.

Referring to FIG. 1, as in the conventional example shown in FIG. 23,the reception system for the PDMA base station includes four antennas 3to 6, frequency converting circuit 7 and A/D converter 8. An inputsignal vector X₁(t) output from A/D converter 8 is applied to a firststage operating apparatus 101, first stage adaptive arrays AA₁₁, . . . ,AA_(k1), . . . , AA_(m1), and to first stage parameter estimators PE₁₁,. . . , PE_(k1), . . . , PE_(m1). Details of the adaptive array will bedescribed later.

Adaptive arrays AA₁₁, . . . , AA_(k1), . . . , AA_(m1) output usersignals Y₁₁(t), . . . , Y_(k1)(t), . . . , Y_(m1)(t) that are complexsignals including with highest intensity the signal component of thecorresponding users (and additionally including interference signalcomponents from other users), respectively, which user signals areapplied to the first stage operating apparatus 101 and detected bycorresponding detectors DE₁₁, . . . , DE_(k1), . . . , DE_(m1).

Parameter estimators PE₁₁, . . . , PE_(k1), . . . , PE_(m1) estimatereception signal coefficient vectors H₁₁, . . . , H_(k1), . . . , H_(m1)of the corresponding users, based on the input signal vector X₁(t) andcorresponding detection outputs of detectors DE₁₁, . . . , DE_(k1), . .. , DE_(m1), and applies the estimated vectors to the first stageoperating apparatus 101. More specifically, each parameter estimatorestimates to what extent the signal component of the corresponding useris included in the input signal vector, to what extent the signalcomponent of the corresponding user has its phase rotated with respectto the input signal vector, and so on.

The first stage operating apparatus 101 subtracts, for each user i (i=1,2, . . . , m), all the user signal components other than the user i ofinterest from the input signal vector X₁(t), so as to eliminate theinterfering signal component, and calculates and outputs further inputsignal vector X_(i2)(t) of the user i. The operation of operatingapparatus 101 will be described in detail later with reference to FIG.2.

The first stage operating apparatus 101 outputs input signal vectorsX₁₂(t), . . . , X_(k2)(t), . . . , X_(m2)(t) corresponding to the users,and applies these to corresponding second stage adaptive arrays AA₁₂, .. . , AA_(k2), . . . , AA_(m2).

User signals Y₁₂(t), . . . , Y_(k2)(t), . . . , Y_(m2)(t) output fromthe second stage adaptive arrays AA₁₂, . . . , AA_(k2), . . . , AA_(m2)are applied to the second stage operating circuit 102 and detected bycorresponding detectors DE₁₂, . . . , DE_(k2), . . . , DE_(m2),respectively.

Parameter estimators PE₁₂, . . . , PE_(k2), . . . , PE_(m2) estimatereception signal coefficient vectors H₁₂, . . . , H_(k2), . . . , H_(m2)of the corresponding users based on the input signal vector X₁(t) andthe corresponding outputs of detectors DE₁₂, . . . , DE_(k2), . . . ,DE_(m2), and applies the estimated vectors to the second stage operatingapparatus 102. Operating apparatus 102 outputs further input signalvectors X₁₃(t), . . . , X_(k3)(t), . . . , X_(m3)(t), and applies tothird stage adaptive arrays AA₁₃, . . . , AA_(k3), . . . , AA_(m3) (notshown).

As a plurality of stages (first stage to Lth stage) of interferencecancellers are provided in series, with each canceller including anadaptive array, a parameter estimator and an operating apparatus, theratio of the signal components of other users included in the usersignals output from respective stages are reduced stepwise, improvingelimination of interference. As a result, communication characteristiccan further be improved.

FIG. 2 is a specific block diagram of the operating apparatus 101 as anexample of the plurality of stages of operating apparatuses shown inFIG. 1. Referring to FIG. 2, operating apparatus 101 includesmultipliers MP₁, . . . , MP_(k−1), MP_(k+1), . . . , MP_(m) and an adderAD_(k). Though not shown for simplicity of description, it is understoodthat, in addition to the shown multipliers and the adder, operatingapparatus 101 includes a multiplier MP_(k) and adders AD₁, . . . ,AD_(k−1), AD_(k+1), . . . , AD_(m).

To the multipliers MP₁, . . . , MP_(k−1), MP_(k+1), . . . , MP_(m), usersignals Y₁₁(t), . . . , Y_((k−1)1)(t), Y_((k+1)1)(t), . . . , Y_(m1)(t)from adaptive arrays AA₁₁, . . . , AA_((k−)), AA_((k+1)), . . . ,AA_(m), as well as reception signal coefficient vectors H₁₁, . . . ,H_((k−1)1), H_((k+1)1), . . . , H_(m1) from parameter estimators PE₁₁, .. . , PE_((k−1)1), PE_((k+1)1), . . . , PE_(m1) are applied.

The outputs of multipliers MP₁, . . . , MP_(k−1), MP_(k+1), . . . ,MP_(m) are applied to a negative input of adder AD_(k), and the inputsignal vector X₁(t) is applied to a positive input of adder AD_(k).Thus, signal components corresponding to users other than user k aresubtracted from input signal vector X₁(t), and the signal componentX_(k2)(t) corresponding to the user k is output from adder AD_(k). Asdescribed above, it is assumed that these adaptive arrays, parameterestimators and an operating apparatus as a whole constitute one stage ofinterference canceller.

As a result, considerable interfering signal components can be removed.By applying the new input vector X_(k2)(t) of which interfering signalcomponents removed considerably by the operating apparatus 101 to thesecond and the following stages of interference cancellers, the ratio ofthe interfering signal components of other users included in the usersignal S_(k)(t) that is finally output can sufficiently be reduced,realizing satisfactory communication characteristic.

To each of the adders not shown, other than adder AD_(k), outputs frommultipliers other than the multiplier corresponding to the adder ofinterest among multipliers MP₁, . . . , MP_(k), . . . , MP_(m) and theinput signal vector X₁(t) are applied in parallel, in the similarmanner. These adders respectively output new input signal vectors shownin FIG. 1 and apply the same to the second and the following stages ofinterference cancellers.

Specific operation of the apparatus shown in FIGS. 1 and 2 will bedescribed in the following.

When we represent the number of antenna elements by n and the number ofusers communicating simultaneously by m, the input signal vector X₁(t)output from A/D converter 8 can be represented by the followingequations.X ₁(t)=[x ₁(t), x ₂(t), . . . x _(n)(t)]^(T)  (1)x _(j)(t)=h _(j1) S ₁(t)+h _(j2) S ₂(t)+ . . . +h _(ji) S _(i)(t)+ . . .h _(jm) S _(m)(t)+n _(j)(t), (j=1, 2, . . . , n)  (2)

The equations (1) and (2) in vector representation provide the followingequation (3).X ₁(t)=H ₁ S ₁(t)+H ₂ S ₂(t)+ . . . +H _(i) S _(i)(t)+H _(m) S_(m)(t)+N(t)  (3)H _(i) =[h _(1i) , h _(2i) , . . . , h _(ni)]^(T), (i=1, 2, . . . ,m)  (4)N(t)=[n _(i)(t), n ₂(t), . . . , n _(n)(t)]^(T)  (5)

The operation in which the new input signal vector X_(k2)(t) is outputfrom operating apparatus 101 of FIG. 2 will be described in greaterdetail.

It is assumed that H_(i) (i=1, 2, . . . , m) can be estimated byparameter estimators PE₁₁, . . . , PE_(k1), . . . , PE_(m1). Further,assuming that the first stage of adaptive arrays AA₁₁, . . . , AA_(k1),. . . , AA_(m1) operate relatively satisfactory, it is possible toregard that Y₁₁(t)≈S_(i)(t).

In this stage, it follows that all the user signals and the receptionsignal coefficient vectors of all the user signals can be obtained.Here, the input signal vector X_(k2)(t) used for signal detection of theuser k for the second stage can be calculated in accordance with theequation (6).X _(k2)(t)=X ₁(t)−H ₁ S ₁(t)− . . . −H_(k−1) S _(k−1)(t)−H _(k+1) S_(k+1)(t)−H _(m) S _(m)(t)  (6)

By substituting the equation (3) for the equation (6), the followingequation (7) results.X _(k2)(t)=H _(k) S _(k)(t)+N(t)  (7)

When X₁(t) is compared with X_(k2)(t), it can be seen that interferingcomponent S_(i)(t) (i=1, 2, . . . m, where i≠k) other than S_(k)(t) isreduced in X_(k2)(t), and therefore, operation of the second stageadaptive arrays is facilitated.

As shown in FIG. 1, in the multistage interference canceller consistingof a plurality of stages of interference cancellers connected to eachother, the reception signal is separated user by user by the adaptivearrays, and the result obtained by removing user signals other than theuser of interest as interfering waves from the reception signal isapplied to the next stage interference canceller, as an input signal ofthe user of interest. As a result, in the next stage interferencecanceller, as the interfering waves of the input user signal arereduced, a user signal with superior communication characteristic can beobtained. By repeating removal of the interfering waves in this mannerover a plurality of stages, the interfering waves can further beremoved, CIR (Carrier to Interference Ratio) can further be improved,and it becomes easier to extract the desired user signal.

Though removal of interfering waves can surely be attained by using theabove described multistage interference canceller, there are thefollowing problems.

(1) In the example of the multistage interference canceller describedabove, the user signal extracted by each adaptive array is removed asthe interfering wave component from the reception signal, withoutdetermining whether there is a demodulation error or not. Therefore, ifthere is a demodulation error in the user signal extracted by anadaptive array and the signal has somewhat deformed waveform, such as animpulse-like waveform, the output of each operating apparatus (inputsignal to the next stage interference canceller) obtained as a result ofsubtraction of such erroneous signal component from the reception signalwould be affected, for example, there would be an impulse-like noise,because of the demodulation error.

(2) As described with reference to FIG. 2, each signal removed fromreception signal X₁(t) by adder AD_(k) is a product of the receptionsignal coefficient vector calculated by each parameter estimator and theuser signal extracted by each adaptive array (hereinafter referred to asa replica signal).

Here, the reception signal coefficient vector calculated by eachparameter estimator does not take into account the correlation valuebetween the user signal of the target user and the user signals of otherusers, and the vector is calculated assuming that the correlation valueis 0.

Actually, there is correlation between a plurality of user signals, andtherefore, the above described calculation method is not well match theactual propagation environment. Therefore, when the reception signalcoefficient vector calculated in accordance with the calculation methodin which the correlation value with the user signals of other users isassumed to be 0 is used to remove the interfering waves, it is possiblethat the output of each operating apparatus (input signal to the nextstage interference canceller) includes an error.

The present invention provides a solution to the problems (1) and (2).

First Embodiment

FIG. 3 is a block diagram representing the reception system for the PDMAbase station in accordance with the first embodiment of the presentinvention.

Referring to FIG. 3, an operating apparatus 101′, first gate units GA,interference removing units IC and second gate units GB, which areprovided for each of a plurality of users, constitute a basicconfiguration of the first stage interference canceller.

Though not shown for the simplicity of description, the first gate unitsGA, interference removing units IC and second gate units GB are providedin the same manner as the first stage interference canceller for aplurality of users, in the succeeding stage of operating unit 102′, sothat operating apparatus 102′ and components GA, IC and GB, not shown,constitute the second stage interference canceller.

Though not shown, succeeding the second stage interference canceller,there are a plurality of interference cancellers configured in the samemanner as the first interference canceller (including the operatingapparatus, first and second gate units and the interference removingunits).

Therefore, the reception system of FIG. 3 is, as a whole, formed bymultistages of interference cancellers, and the outputs of the secondgate unit GB (not shown) provided for the plurality of users of the laststage interference canceller are provided as the final outputs of thereception system.

As in the reception system shown in FIG. 1, the input signal vectorX₁(t) is output from A/D converter 8, applied to operating apparatus101′ of the first stage interference canceller, and commonly applied tothe plurality of interference canceling units IC₁₁, . . . , IC_(k1), . .. , IC_(m1) provided corresponding to the plurality of users in apreceding stage of the first stage interference canceller.

In the reception system shown in FIG. 3, the interference removing unitsIC all have the same configuration and, as an example, the configurationof interference removing unit IC_(k1) is shown in FIG. 4.

Referring to FIG. 4, the complex signal of the user k extracted byadaptive array AA_(k1) from the input signal vector X₁(t) input tointerference removing unit IC_(k1) is converted to a bit informationsignal by a demodulator DM_(k1). The bit information signal is appliedto an error determining unit ED_(k1) as well as to a re-modulatorRM_(k1).

Error determining unit ED_(k1) determines whether there is ademodulation error in the extracted signal from adaptive array AA_(k1),based on the bit information signal from demodulator DM_(k1). When it isdetermined that there is a demodulation error, an error determinationsignal E_(k1) at the L level is generated and applied to the operatingapparatus 101′ of the first stage interference canceller.

Re-modulator RM_(k1) again converts the bit information signal fromdemodulator DM_(k1) to the user signal Y_(k1)(t), which is a complexsignal, and applies the same to operating apparatus 101′ of the firststage interference canceller as well as to the parameter estimatorPE_(k1).

Parameter estimator PE_(k1) calculates the reception signal coefficientvector H_(k1) of the corresponding user based on the input signal vectorX₁(t) and the user signal Y_(k1)(t), and applies the calculated vectorto operating apparatus 101′ of the first stage interference canceller.

The arrangement including the adaptive array, a demodulator, an errordetermining unit, a re-modulator and a parameter estimator such as shownin FIG. 4 is common to all the interference removing units IC shown inFIG. 3, and therefore, overlapping description would not be repeated.

FIG. 5 is a block diagram representing a specific configuration ofoperating apparatus 101′ of the first stage interference canceller, asan example of the plurality of stages of interference cancellersconstituting the reception system shown in FIG. 3. Referring to FIG. 5,operating apparatus 101′ includes multipliers MP₁, . . . , MP_(k−1),MP_(k), MP_(k+1), . . . , MP_(m), AND gates AND₁, . . . , AND_(k−1),AND_(k), AND_(k+1), . . . , AND_(m) and an adder AD.

To multipliers MP₁, . . . , MP_(k−1), MP_(k), MP_(k+1), . . . , MP_(m),user signals Y₁₁(t), . . . , Y_((k−1)1)(t), Y_(k1)(t), Y_((k+1)1)(t), .. . , Y_(m1)(t) from the preceding stage interference removing unitsIC₁₁, . . . , IC_((k−1)1), IC_(k1), IC_((k+1)1), . . . , IC_(m1), andreception signal coefficient vectors H₁₁, . . . , H_((k−1)1), H_(k1),H_((k+1)1), . . . , H_(m1) are applied. Outputs of multipliers MP₁, . .. , MP_(k−1), MP_(k), MP_(k+1), . . . , MP_(m) are applied to one inputsof corresponding AND gates AND₁, . . . , AND_(k−1), AND_(k), AND_(k+1),. . . , AND_(m), respectively, and corresponding error determinationsignals E₁₁, . . . , E_((k−1)1), E_(k1), E_((k+1)1), . . . , E_(m1) fromthe preceding stage interference removing units IC₁₁, . . . ,IC_((k−1)1), IC_(k1), IC_((k+1)1), . . . , IC_(m1) are input to theother inputs of these AND gates.

Outputs of AND gates AND₁, . . . , AND_(k−1), AND_(k), AND_(k+1), . . ., AND_(m) are applied to negative inputs of adder AD, and the inputsignal vector X₁(t) from A/D converter 8 is applied to a positive inputof adder AD.

The output of adder AD is provided from operating apparatus 101′ asinput signal vector X₂(t), which is commonly applied to the first gateunits GA₁₂, . . . , GA_(k2), . . . , GA_(m2) corresponding to theplurality of users, respectively, as shown in FIG. 3.

Though not shown in the block diagram of operating apparatus 101′ ofFIG. 5, the reception signal coefficient vectors H₁₁, . . . , H_(k1), .. . , H_(m1), the error determination signals E₁₁, . . . , E_(k1), . . ., E_(m1) and the user signals Y₁₁(t), . . . , Y_(k1)(t), . . . ,Y_(m1)(t) output from respective interference units IC₁₁, . . . ,IC_(k1), IC_(m1) of the preceding stage are passed through operatingapparatus 101′ as they are, and applied to the corresponding first gateunits GA₁₂, . . . , GA_(k2), . . . , GA_(m2) of the first stageinterference canceller, user by user.

Now, referring to FIG. 5, an L level error determination signal E₁₁ fromerror determining unit ED₁₁ of interference removing unit IC₁₁ thatcorresponds to the user signal, e.g., the signal Y₁₁(t), which isdetermined to have a demodulation error by the preceding stageinterference removing unit as described above, is applied to the otherinput of the corresponding AND gate AND₁ of operating apparatus 101′. Asa result, this AND gate is closed, and input of the product between thereception signal coefficient vector H₁₁ and the user signal Y₁₁(t)output from the corresponding multiplier MP₁, that is, input of thereplica signal to adder AD is prevented.

As a result, from the interference wave components (replica signals) ofrespective users to be subtracted from input signal vector X₁(t), theinterference wave component (replica signal) corresponding to the usersignal that includes a demodulation error is excluded. As a result, theimpulse-like noise, for example, will not be included in the inputsignal vector X₂(t) output from operating apparatus 101′ of the firststage interference canceller.

In the first stage interference canceller, the error signal E₁₁ that haspassed through operating apparatus 101′ from the preceding stageinterference removing unit IC₁₁ is applied to a selective control inputof the first gate unit GA corresponding to each user, gate unit GA₁₂corresponding to user 1, for example.

When it is determined by the preceding stage interference removing unitIC₁₁ that there is an error, the first gate unit GA₁₂ selects, inaccordance with the error determination signal E₁₁, the input signalvector X₂(t) of high precision not including any noise, that is newlycalculated by operating apparatus 101′ and applies the same tointerference removing unit IC₁₂.

As already described with respect to IC_(k1) of FIG. 4 above, theinterference removing unit IC₁₂ newly calculates, based on the inputsignal vector X₂(t), a reception signal coefficient vector H₁₂, an errordetermination signal E₁₂ and a user signal Y₁₂(t), which are applied tothe second gate unit GB₁₂.

When it is determined by the preceding stage interference removing unitIC₁₁ that there is no error, the first gate unit GA₁₂ selects andapplies to the second gate unit GB₁₂ the reception signal coefficientvector H₁₁, the error determination signal E₁₁ and the user signalY₁₁(t) that have passed through operating unit 101′, in accordance withthe error determination signal E₁₁.

To the selective control input of the second gate unit GB₁₂, the errordetermination signal E₁₁ is commonly applied to the first gate unitGA₁₂. When it is determined by the preceding stage interference removingunit IC₁₁ that there is an error, the second gate unit GB₁₂ selects andoutputs the reception signal coefficient vector H₁₂, the errordetermination signal E₁₂ and the user signal Y₁₂(t) that are newlycalculated by interference removing unit IC₁₂ in accordance with theerror determination signal E₁₁, and applies these to operating apparatus102′ constituting the second stage interference canceller.

When it is determined by the preceding stage interference removing unitIC₁₁ that there is no error, the second gate unit GB₁₂ selects andoutputs the reception signal coefficient vector H₁₁, error determinationsignal E₁₁ and the user signal Y₁₁(t) transmitted from the first gateunit GA₁₂ as they are, in accordance with the error determination signalE₁₁, and applies these as the reception signal coefficient vector H₁₂,the error determination signal E₁₂ and the user signal Y₁₂(t), tooperating apparatus 102′ constituting the second stage interferencecanceller.

The same operation is performed by the gate units GA, GB and theinterference removing units IC corresponding to users other than user 1,and therefore, description thereof will not be repeated.

In summary, in the above described operation, among the preceding stageinterference removing units IC receiving the input signal vector X₁(t),to the user determined to be free of any error, the reception signalcoefficient vector H, the error determination signal E and a user signalY(t) calculated by the interference removing unit IC are directly passedthrough the operating unit 101′, the first gate unit GA and a second GBof the first stage interference canceller and applied to the secondstage interference canceller. More specifically, for the user oncedetermined to be free of any error by the interference removing unit IC,nothing is applied to the interference removing unit IC of thesucceeding stage of the interference cancellers, and the receptionsignal coefficient vector H, the error determination signal E and theuser signal Y(t) are not newly calculated.

Among the preceding stage interference removing units IC receiving theinput signal vector X₁(t), to the user determined to have an error, theinterference removing unit IC of the first stage newly calculates thereception signal coefficient vector H, the error determination signal Eand the user signal Y(t) and applies to the second stage interferencecanceller, based on the input signal vector X₂(t) from which theinterference wave is removed with high precision without introducing anynoise by the operating apparatus 101′ of the first stage interferencecanceller.

The operating apparatus 102′ of the second stage interference cancellerhas the identical configuration as the operating apparatus 101′ of thefirst stage interference canceller, and performs the same operation asthat described with reference to FIG. 5. More specifically, only thereplica signal corresponding to the user signal not including anydemodulation error is subtracted from the initial input signal vectorX₁(t), and the next input signal vector X₃(t) is output from adder AD(FIG. 5).

More specifically, for the user once determined to be free of any errorby the preceding stage interference removing units IC₁₁, . . . ,IC_(k1), . . . , IC_(m1), the replica signal thereof is always theobject of subtraction from the initial input signal vector X₁(t) at theinterference canceller of any succeeding stage.

On the other hand, even when the user has been excluded from the objectof subtraction from the initial input signal vector X₁(t) at theoperating apparatus 101′ of the first stage interference canceller as itis determined to include an error by the preceding stage interferenceremoving units IC₁₁, . . . , IC_(k1), . . . , IC_(m1), if it isdetermined to be free of any error by any of the interference removingunits IC₁₂, . . . , IC_(k2), . . . , IC_(m2) of the first stageinterference canceller, then the replica signal thereof is always anobject of subtraction from the initial input signal vector X₁(t) in theinterference canceller of any of the succeeding stages.

As a result, in operating apparatus 102′ of the second stageinterference canceller, an input signal vector X₃(t) can be obtained,from which interference wave is removed with higher precision withoutintroducing any noise.

The operation of the second stage interference canceller includingoperating apparatus 102′ is completely the same as that of the firststage interference canceller described above which includes operatingapparatus 101′, the first gate units GA₁₂, . . . , GA_(k2), . . . ,GA_(m2), interference removing units IC₁₂, . . . , IC_(k2), . . . ,IC_(m2), and the second gate units GB₁₂, . . . , GB_(k2), . . . ,GB_(m2).

By connecting a plurality of stages of such interference cancellers inseries, and by subtracting only the replica signal of the user which isdetermined to be free of any error from the initial input signal vectorX₁(t) at the operating apparatus of the interference canceller of eachstage, it becomes possible to remove the interfering waves with highprecision, at the interference canceller of each stage.

For the user once determined to be free of any error by the interferenceremoving unit IC in any of the stages including the preceding stage, thereception signal vector H, the error determination signal E and the usersignal Y(t) calculated by that interference removing unit IC are outputfrom the second gate unit GB (not shown) of the interference cancellerof the last stage, and from which, the user signal Y(t) is extracted andoutput from the reception system as the final, error-free user signal.

For the user determined to include an error by the interference removingunit IC of every stage, the reception signal coefficient vector H, theerror determination signal E and the user signal Y(t) calculated by theinterference removing unit IC of the interference canceller of the laststage are output from the second gate unit GB, and from which the usersignal Y(t) is extracted and output from the reception system as thefinal user signal with an error.

The effect of the first embodiment will be more specifically described.The above described first embodiment is configured such that in eachstage of the multiple stages of interference cancellers, theinterference component corresponding to (error-free) user, that is, thereplica signal, is removed from the initial input signal X₁(t) by theoperating apparatus. The first embodiment having such a configurationprovides the following effects.

For example, assume that a reception signal of user 4 is to be foundamong four users. When users 1 and 2 only are determined to be free ofany demodulation error by the preceding stage interference removingunits IC₁₁ and IC₁₂, only the replica signals of users 1 and 2 aresubtracted from the initial input signal vector X₁(t) by the operatingapparatus 101′ of the first stage interference canceller. As a result,the reception signal X₂(t) for the user 4 from the first stageinterference canceller will be

Initial input signal−(replica signal of user 1+replica signal of user2).

Next, if it is determined that user 3 is also free of any demodulationerror in addition to users 1 and 2, by the interference removing unitIC₃₂ of the first stage, the replica signals of users 1, 2 and 3 aresubtracted from the initial input signal X₁(t) by the operatingapparatus 102′ of the second stage interference canceller. As a result,the reception signal X₃(t) for the user 4 of the second stageinterference canceller will be

Initial input signal−(replica signal of user 1+replica signal of user2+replica signal of user 3).

Second Embodiment

FIG. 6 is a block diagram representing the reception system for the PDMAbase station in accordance with the second embodiment of the presentinvention. Different from the reception system in accordance with thefirst embodiment shown in FIG. 3 in which the replica signal issubtracted from the initial input signal vector X₁(t) by the operatingapparatus of the interference canceller of each stage, the receptionsystem in accordance with the second embodiment is configured such thatthe interference component corresponding to each user, that is, thereplica signal, is subtracted from an input signal vector that is newlycalculated by the operating apparatus of the interference canceller ofeach stage.

The reception system in accordance with the second embodiment shown inFIG. 6 differs from the reception system in accordance with the firstembodiment shown in FIG. 3 in the following points. Namely, in the firststage interference canceller including operating apparatus 101′, gateunits GA₁₂, . . . , GA_(k2), . . . , GA_(m2) and interference removingunits IC₁₂, . . . , IC_(k2), . . . , IC_(m2), the input signal vectorX₂(t) output from operating apparatus 101 is applied, instead of X₁(t)of FIG. 3, to the operating apparatus 102″ of the second stageinterference canceller. Further, in FIG. 6, the second gate unit GAshown in FIG. 3 is not provided. The reception signal coefficient vectorX, error signal E and user signal Y(t) as the outputs of interferenceremoving unit IC and the reception signal vector H, the errordetermination signal E and the user signal Y(t) passed from thepreceding stage interference removing unit IC through gate unit GA areapplied in parallel, to the operating apparatus 102″ of the second stageinterference canceller.

The operating apparatus 102″ of the second stage interference canceller(and operating apparatuses of interference cancellers of the followingstages) has such a configuration as shown in FIG. 7, and not theconfiguration shown in FIG. 5 described above.

In operating apparatus 102″ shown in FIG. 7, the reception signalcoefficient vector H₁₂, the error determination signal E₁₂ and the usersignal Y₁₂(t) from the interference removing unit IC of the precedingstage interference canceller, for example, from interference removingunit IC₁₂, and the reception signal coefficient vector H₁₁, the errordetermination signal E₁₁ and the user signal Y₁₁(t) that have passedthrough the first stage interference canceller from the preceding stageinterference removing unit IC₁, are applied to gate unit GC₁.

To the selective control input of gate unit GC₁, the error determinationsignal E₁₁ is applied. When error determination signal E₁₁ representsabsence of any error, then the reception signal coefficient vector H₁₁,the error determination signal E₁₁ and the user signal Y₁₁(t) frominterference removing unit IC₁₁ are selected and output as the receptionsignal coefficient vector H₁₂, the error determination signal E₁₂ andthe user signal Y₁₂(t) and, when the error determination signal E₁₁represents presence of an error, the reception signal coefficient vectorH₁₂, the error determination signal E₁₂ and the user signal Y₁₂(t) frominterference removing unit IC₁₂ are selected and output.

The reception signal coefficient vector H₁₂ and user signal Y₁₂(t) fromthe interference removing unit IC₁₂ of the first stage interferencecanceller are multiplied by multiplier MP₁, and an output thereof isapplied to one input of AND gate AND₁. To the other input of AND gateAND₁, the error determination signal E₁₂ from interference removing unitIC₁₂ is applied.

Between AND gate AND₁ and adder AD, a gate unit GD₁ is provided, and theerror determination signal E₁₁ is input to the selective control inputof gate unit GD₁. When the error determination signal E₁₁ representsabsence of any error, gate unit GD₁ is closed, so that the output of ANDgate AND₁ is not applied to the negative input of adder AD. When errordetermination signal E₁₁ represents presence of an error, gate unit GD₁is opened, applying the output of AND gate AND₁ to the negative input ofadder AD.

To the positive input of adder AD, not the initial input signal vectorX₁(t) applied in the first embodiment but the input signal vector X₂(t)calculated by operating apparatus 101′ of the preceding stageinterference canceller is input.

Though the configuration corresponding to user 1 has been described, itis understood that the operating apparatus 102″ has the sameconfiguration for users 1 to m.

The operation of the reception system in accordance with the secondembodiment having the above described configuration is as follows. Amongthe preceding stage interference removing units IC₁₁, . . . , IC_(k1),IC_(m1) receiving the input signal vector X₁(t), for the user determinedto be free of any error, the reception signal vector H, the errordetermination signal E and the user signal Y(t) calculated by theinterference removing unit IC of interest are directly passed throughthe operating unit 101′ and the gate unit GA of the first stageinterference canceller as well as the operating unit 102″ and the gateunit GC of the second unit interference canceller, and applied to thegate unit GA of the second stage interference canceller (not shown).

Namely, for the user once determined to be free of any error by thepreceding stage interference removing unit IC, nothing is applied to thesucceeding stage interference removing unit IC.

For the user determined to have an error among the preceding stageinterference removing units IC₁₁, . . . , IC_(k1), . . . , IC_(m1)receiving the input signal vector X₁(t), based on the input signalvector X₂(t) from which the interfering wave has been removed with highprecision without introducing any noise by operating apparatus 101′ ofthe first stage interference canceller, the interference removing unitIC of the first stage interference canceller newly calculates thereception signal coefficient vector H, the error determination signal Eand the user signal Y(t) and applies these to the operating apparatus102″ of the second stage interference canceller (FIG. 7).

In the operating apparatus 102″ of the second stage interferencecanceller, only the replica signal corresponding to the user determinedby the interference removing unit IC of the preceding stage (firststage) interference canceller to be free of any demodulation error issubtracted from input signal vector X₂(t) output from the operatingapparatus 101′ of the preceding stage interference canceller.

Here, for the user 1 determined to be free of any error by any of thepreceding stage interference removing units IC₁₁, . . . , IC_(k1), . . ., IC_(m1), for example, by interference removing unit IC₁₁, the replicasignal thereof has been already subtracted from initial input signalvector X₁(t) by operating apparatus 101′, and it is not included anymorein the input signal vector X₂(t) applied to the adder AD of operatingapparatus 102″. For the user 1 determined to be free of any error, thereception signal coefficient vector H₁₁, the error determination signalE₁₁ and the user signal Y₁₁(t) as the outputs of the preceding stageinterference removing unit IC₁₁ are selected, passed through the gateunit GC₁ of operating apparatus 102″ and output to the succeeding stage.Therefore, to the interference removing unit IC₁₂ of the first stageinterference canceller corresponding to user 1, X₂(t) is not applied,and the reception signal coefficient vector H₁₂, the error determinationsignal E₁₂ and user signal Y₁₂(t) are not provided.

Therefore, for the user already determined to be free of any error, theoperation by multiplier MP₁ and AND gate AND₁ are not performed, andsubtraction from the input signal vector X₂(t) by adder AD is excluded.Even when the input X₂(t) to interference removing unit IC₁₂ is 0, inorder to prevent generation of any noise by the operation ofinterference removing unit IC₁₂ and input of the noise to adder ADthrough multiplier MP₁ and AND gate AND₁, gate unit GD₁ is closed forthe user 1 determined to be free of any error, and the output from ANDgate AND₁ to adder AD is completely shut out.

The effect of the second embodiment will be more specifically described.According to the second embodiment, the interference canceller of eachstage is configured to remove the replica signal from the input signalvector calculated by the operating apparatus of one stage, by theoperating apparatus of the next stage.

For example, assume that a reception signal of user 4 is to be foundamong four users. When it is determined that users 1 and 2 only aredetermined to be free of error by the preceding stage interferenceremoving units IC₁₁ and IC₂₁, the reception signal vector X₂(t) for theuser 4 of the first stage interference canceller will be

Initial input signal−(replica signal of user 1+replica signal of user2).

In accordance with the second embodiment, the reception signal for user4 of the second stage interference canceller will be

X₂(t)−(replica signal of user 3).

More specifically, in the first embodiment described above, the replicasignal is subtracted from the initial input signal vector X₁(t) at theoperating apparatus of the interference canceller of each stage.Therefore, the replica signal of a user once subtracted as being free ofany error must be again subtracted from the input signal vectorrepeatedly at each succeeding stage. In the second embodiment, for theuser already subtracted from the input signal vector as being free ofany error, it is unnecessary to repeat subtraction from the input signalvector at the succeeding stages. Therefore, according to the secondembodiment, the amount of calculation can significantly be reduced.

Third Embodiment

FIG. 8 is a block diagram representing a reception system for the PDMAbase station in accordance with the third embodiment of the presentinvention. In the third embodiment, basically, from the reception signalvector X_(1k)(t) used for signal detection for the user k at the kthstage interference removing unit IC_(1k) in the longitudinal direction,a value obtained by multiplying the detected signal Y_(1k)(t) of theuser k and the reception signal coefficient vector H_(1k) output from aparameter estimator is subtracted, and thus obtained signal vector isused as the input signal vector X_(1(k+1))(t) of the adaptive array ofthe (k+1)th interference removing unit IC_(1(k+1)). Thus, the usersignal Y_(1(k+1))(t) is extracted more accurately in the interferenceremoving unit of the next stage.

More specifically, the input signal vector X₁₁(t) output from A/Dconverter 8 is applied to the interference removing unit IC₁₁ of thefirst stage. In FIG. 8, interference removing units ICs all have thesame configuration, and as an example, the configuration of interferenceremoving unit IC_(1k) is shown in FIG. 9.

Referring to FIG. 9, the input signal vector X_(1k)(t) applied from theinterference removing unit IC_(1(k−1)) of the preceding stage is inputto adaptive array AA_(1k) as well as to the positive input of adderAD_(1k) and a parameter estimator PE_(1k). By adaptive array AA_(1k),the user signal Y_(1k)(t) as a complex signal is extracted from inputsignal vector X_(1k)(t), and converted by demodulator DM_(1k) to a bitinformation signal. The bit information signal is applied to errordetermining unit ED_(1k) as well as to re-modulator RM_(1k). Based onthe applied bit information signal, error determination unit ED_(1k)determines whether there is a demodulation error in the extracted signalfrom adaptive array AA_(1k). When it is determined that there is anerror, an L level error determination signal E_(1k) is generated andexternally output. Re-modulator RM_(1k) converts the applied bitinformation signal again to the user signal Y_(1k)(t) as a complexsignal and outputs. The user signal Y_(1k)(t) is applied to parameterestimator PE_(1k) and multiplier MP_(1k) and, in addition, externallyoutput.

Parameter estimator PE_(1k) estimates the reception signal coefficientvector H_(1k), based on the detected user signal Y_(1k)(t) and the inputsignal vector X_(1k)(t). Multiplier MP_(1k) multiplies the receptionsignal coefficient vector H_(1k) and user signal Y_(1k)(t), and appliesthe result to a negative input of under AD_(1k). Between multiplierMP_(1k) and adder AD_(1k), an AND gate AND_(1k) is provided, and to oneinput thereof, error determination signal E_(1k) is applied from errordetermination unit ED_(1k).

Referring to FIG. 8, corresponding to users 1 to m, interferenceremoving units IC₁₁, . . . , IC_(1m) are connected in series in thelongitudinal direction, and m interference removing units constitutesthe interference canceller of the first stage. The interference removingunit IC of each stage is configured in the similar manner as theinterference removing unit of the kth stage of FIG. 9, and therefore,description thereof will not be repeated.

The basic operation of the third embodiment shown in FIGS. 8 and 9 willbe described in the following. Equations (1) to (5) described withreference to the reception system as the basic concept of the presentinvention shown in FIGS. 1 and 2 are also applied to the thirdembodiment.

First, the user signal output from the interference removing unitIC_(1k) of the kth stage is Y_(1k)(t). Parameter estimator PE_(1k)outputs the reception signal coefficient vector H_(1k) of user k, fromuser signal Y_(1k)(t) of the user k and the input signal vectorX_(1k)(t). Multiplier MP_(1k) multiplies the user signal Y_(1k)(t) bythe reception signal coefficient vector H_(1k), and the result issubtracted by adder AD_(1k) from input signal vector X_(1k)(t). Theresult is used as the input signal vector X_(1(k+1))(t) to theinterference removing unit IC_(1(k+1)) of the next stage. Namely, thefollowing equation is obtained.X _(1(k+1))(t)=X ₁(t)−H _(1k) S _(1k)(t)  (9)

By substituting the above described equation (3) for equation (9), thefollowing equation (10) results.X _(1(k+1))(t)={H _(1k) Y _(1k)(t)+H _(1(k+1)) Y _(1(k+1))(t)+ . . . +H_(1m)(t)+N(t)}H _(1k) Y _(1k)(t)=H _(1(k+1)) Y _(1(k+1))(t)+ . . . +H_(1m) S _(1m)(t)+N(t)  (10)

As can be understood from the equation (10), the input vector signalX_(1(k+1))(t) is a vector signal corresponding to the input vectorsignal X_(1k)(t) of the interference removing unit of the precedingstage with the component of the user signal Y_(1k)(t) (that is,interference signal component for the adaptive array AA_(1(k+1)) of theinterference removing unit of the k+1th stage) removed. Therefore, whenX_(1(k+1))(t) rather than X_(1k)(t) is used as the input signal vectorfor the adaptive array AA_(1(k+1)) of the interference canceller of thek+1th stage, the adaptive array operates better, and as a result, moreaccurate signal Y_(1(k+1))(t) of the user (k+1) can be extracted.

In the reception system in accordance with the third embodiment shown inFIGS. 8 and 9, when the user signal extracted by the adaptive arrayAA_(1k) of each stage (for example, kth stage) of the interferencecanceller of the first stage includes a demodulation error, errordetermining unit ED_(1k) generates an L level error determination signalE_(1k) and applies the same to one input of AND gate AND_(1k).Therefore, input of the product of the reception signal coefficientvector H_(1k) and the user signal Y_(1k)(t) output from multiplierMP_(1k), that is, input of replica signal to adder AD_(1k) can beprevented.

As a result, of the processings for subtracting interference wavecomponents performed by adders AD₁₁, . . . , AD_(1k), . . . , AD_(1m) ofrespective stages, subtraction of the extracted user signal with anerror is excluded, and therefore, such an error is not reflected (forexample, an impulse-like noise is not generated) in the result ofsubtraction at each stage. Therefore, the influence of the demodulationerror on the user signal output from each stage can be prevented.

As described above, in the interference canceller of the first stageincluding a series connection of interference removing units IC₁₁, . . ., IC_(1m), at the interference removing unit where it is determined thatthere is an error, removal of the interfering wave is stopped.Therefore, from the view point of removing interference wave component,it may be insufficient. It is noted, however, that when the user signalincluding a demodulation error is once subtracted, the user outputsignals of all the succeeding stages are affected, providing aninaccurate output signal. In view of such a drawback, the interferencecanceller including k stages of interference removing units in thelongitudinal direction is considered sufficiently effective, in that itensures validity of the output user signal, though removal of theinterference wave component is somewhat insufficient.

In the third embodiment shown in FIG. 8, however, in order to furtherpromote removal of the interfering wave component, the series connectionof interference removing units IC₁₁, . . . , IC_(1m) of longitudinal kstages form a first stage interference canceller, and a plurality ofsuch first stage interference cancellers are connected in the lateraldirection, so that an interference canceller of multiple stages as awhole is provided. This enables further removal of the interference wavecomponent for the processing of the succeeding stages.

More specifically, an error determination signal output from each stageof any one of a plurality of users 1 to m, for example, an errordetermination signal E₁₁ output from interference removing unit IC₁₁ ofthe first stage in the longitudinal direction is applied to an input ofthe gate unit GE₂₁ of the first stage of the next stage interferencecanceller adjacent in the lateral direction, as well as to selectivecontrol inputs of gate units GF₂₁ and GG₂₁. Further, the user signalY₁₁(t) output from interference removing unit IC₁₁ is also applied tothe input of gate unit GE₂₁.

The input signal vector X₂₁(t) from interference removing unit IC_(1m)of the last stage of the first stage interference canceller is alsoapplied to the input of gate unit GE₂₁.

When error determination signal E₁₁ indicates that there is nodemodulation error at the interference removing unit IC₁₁, gate unitGE₂₁ passes the error determination signal E₁₁ itself and the usersignal Y₁₁(t) as they are and apply these signals to the input of gateunit GF₂₁, and applies the input signal vector X₂₁(t) to the input ofgate unit GG₂₁, in accordance with the input error determination signalE₁₁.

When the error determination signal E₁₁ indicates that there is ademodulation error at interference removing unit EC₁₁, gate unit GE₂₁applies the input signal vector X₂₁(t) to the input of interferenceremoving unit IC₂₁, in accordance with the input error determinationsignal E₁₁.

Interference removing unit IC₂₁ has the same configuration as theinterference removing unit IC_(1k) shown in FIG. 9, which applies thecalculated error determination signal E₂₁ and the user signal Y₂₁(t) tothe input of gate unit GF₂₁, and applies the input signal vector X₂₂(t)to the input of gate unit GG₂₁.

When error determination signal E₁₁ represents absence of any error,gate unit GF₂₁ selects the error determination signal E₁₁ and a usersignal Y₁₁(t) that have passed through gate unit GE₂₁ from theinterference removing unit IC₁₁ of the preceding stage, and outputsthese as error determination signal E₂₁ and the user signal Y₂₁(t),respectively.

When error determination signal E₁₁ represents presence of an error,gate unit GF₂₁ selects the error determination signal E₂₁ and the usersignal Y₂₁(t) newly calculated by interference removing unit IC₂₁ andoutputs these as they are.

When the error determination signal E₁₁ represents absence of any error,gate unit GG₂₁ selects the input signal vector X₂₁(t) that has passedthrough gate unit GE₂₁ from interference removing unit IC_(1m), andapplies the same to the input of gate unit GE₂₂ of the succeeding stage.

When error determination signal E₁₁ represents presence of an error,gate unit GG₂₁ selects the input signal vector X₂₂(t) newly calculatedby interference removing unit IC₂₁, and applies the same to the input ofgate unit GE₂₂ of the succeeding stage.

More specifically, when it is once determined by the interferenceremoving unit IC₁₁ of the preceding stage interference canceller thatthere is no error, the error determination signal E₁₁ and the usersignal Y₁₁(t) calculated by the interference removing unit IC₁₁ arepassed as they are through the interference cancellers connected in aplurality of stages in the lateral direction, and output as finaloutputs from the gate GF (not shown) of the interference canceller ofthe last stage. Further, the input signal vector X₂₁(t) from thepreceding stage is directly applied to the input of gate unit GG₂₁, notthrough the interference removing unit IC₂₁.

When it is determined by the interference removing unit IC₁₁ of thepreceding stage interference canceller that there is an error, itfollows that the input signal vector X₂₁(t) input to the interferenceremoving unit IC₂₁ still includes the interference component of user 1,as subtraction of the replica signal corresponding to user 1 from theinput signal vector is inhibited in the interference removing unit IC₁₁.Therefore, interference removing unit IC₂₁ newly performs removal of theinterference wave component of user 1, based on the input signal vectorX₂₁(t) from which the interference wave component has been alreadyremoved for the error-free users. The operation of interference removingunit IC₂₁ is as already described with reference to FIG. 9.

The user signal Y₂₁(t) and the error determination signal E₂₁representing presence/absence of a demodulation error at theinterference removing unit IC₂₁ output from the first stage interferenceremoving unit IC₂₁ corresponding to user 1 are applied through gate unitGF₂₁ to the input of gate unit GE (not shown) of the interferencecanceller of the next stage. Dependent on the presence/absence of theerror at the preceding stage interference removing unit IC₁₁, the inputsignal vector X₂₂(t) newly calculated by interference removing unit IC₂₁or the input signal vector X₂₁(t) directly output from the precedingstage interference removing unit IC_(1m) through gate unit GE₂₁ isapplied to the gate unit GE₂₂ of the succeeding stage. The input signalvector X₂₂(t) is applied to interference removing unit IC₂₂ or furtherpassed to the next stage through gate unit GG₂₂ without passing throughinterference removing unit IC₂₂, depending on presence/absence of theerror at the interference removing unit IC₁₂.

The configuration and the operation of the second stage corresponding touser 2 are the same as the configuration and the operation of the firststage corresponding to user 1 described above.

Thus, according to the third embodiment of the present invention, aninterference canceller is formed by m stages of interference removingunits corresponding to users 1 to m connected in series in thelongitudinal direction and a plurality of stage of such carriers areprovided in the lateral direction, so that the interference wavecomponent can further be removed.

Fourth Embodiment

FIG. 10 is a block diagram representing the reception system for thePDMA base station in accordance with the fourth embodiment of thepresent invention. The configuration of the reception system shown inFIG. 10 is the same as the reception system in accordance with the firstembodiment shown in FIG. 3, except for the following points.

In the first embodiment shown in FIG. 3, the user signal that is acomplex signal output from the re-modulator (FIG. 4) included in eachinterference removing unit IC is applied only to the parameter estimator(FIG. 4) included in that interference removing unit, and not applied tothe parameter estimators of the interference removing units of otherusers. In the fourth embodiment shown in FIG. 10, the user signal outputfrom the re-modulator of the interference removing unit of each user isapplied not only to the user of interest but also to the parameterestimators of interference removing units of all other users.

As described with reference to the reception system as a basic conceptfor the present invention shown in FIG. 1, when the reception signalcoefficient vector is estimated without taking into consideration thecorrelation value between the user signal of a user of interest and theuser signals of other users (assuming that the correlation value is 0),it may cause an error in the output signal.

In the fourth embodiment shown in FIG. 10, the reception signalcoefficient vector of each user is estimated, taking into considerationthe correlation value among a plurality of user signals. The method ofcalculation will be described in the following.

For example, it is assumed that the reception signal X₁(t) is defined inthe following manner, by the signals Y₁₁(t), Y₂₁(t), Y₃₁(t), Y₄₁(t) offour users and the reception signal coefficient vectors H₁₁, H₂₁, H₃₁and H₄₁.

$\begin{matrix}{{X_{1}(t)} = {\left( {H_{11}*{Y_{11}(t)}} \right) + \left( {H_{21}*{Y_{21}(t)}} \right) + \left( {H_{31}*{Y_{31}(t)}} \right) + \left( {H_{41}*{Y_{41}(t)}} \right) + n}} & (11)\end{matrix}$where n represents a noise component.

Here, when an ensemble average between the user signal Y₁₁(t) of user 1and a reception signal X₁(t) is calculated, the equation (11) can bedeveloped in the following manner. Here, “*” as a suffix represents acomplex conjugate.

$\begin{matrix}{{E\left\lbrack {{X_{1}(t)}*{Y_{11}(t)}} \right\rbrack} = {{H_{11}*{E\left\lbrack {{Y_{11}(t)}*Y_{11}*(t)} \right\rbrack}} + {H_{21}*{E\left\lbrack {{Y_{21}(t)}*Y_{11}*(t)} \right\rbrack}} + {H_{31}*{E\left\lbrack {{Y_{31}(t)}*Y_{11}*(t)} \right\rbrack}} + {H_{41}*{E\left\lbrack {{Y_{41}(t)}*Y_{11}*(t)} \right\rbrack}} + {E\left\lbrack {n*Y_{11}*(t)} \right\rbrack}}} & (12)\end{matrix}$

Here, E[Y₁₁(t)*Y₁₁*(t)]=1, [n*Y₁₁*(t)]=0, and therefore, equation (12)can be represented as

$\begin{matrix}{{E\left\lbrack {{X_{1}(t)}*Y_{11}*(t)} \right\rbrack} = {H_{11} + {H_{21}*{E\left\lbrack {{Y_{21}(t)}*Y_{11}*(t)} \right\rbrack}} + {H_{31}*{E\left\lbrack {{Y_{31}(t)}*Y_{11}*(t)} \right\rbrack}} + {H_{41}*{E\left\lbrack {{Y_{41}(t)}*Y_{11}*(t)} \right\rbrack}}}} & (13)\end{matrix}$

In the reception system as a basic concept for the present inventionshown in FIGS. 1 and 2, the correlation values E[Y₂₁(t)*Y₁₁*(t)],E[Y₃₁(t)*Y₁₁*(t)] and E[Y₄₁(t)*Y₁₁*(t)] among the user signals, whichare correlated in the actual propagation environment, have been assumedto 0. Therefore, the resulting value E[X₁(t)*Y₁₁*(t)]=H₁₁ includes anerror. In the fourth embodiment, the correlation values among the users(ensemble average) are actually calculated, and then, the receptionsignal coefficient vectors H₁₁, H₂₁, H₃₁ and H₄₁ are calculated. Thefollowing calculation is executed by parameter estimators PE₁₁, . . . ,PE_(k1), . . . , PE_(m1) at the interference removing units IC₁₁, . . ., IC_(k1), . . . , IC_(m1) of the preceding stage, for example.

More specifically, when the reception signal coefficient vectors H₁₁,H₂₁, H₃₁ and H₄₁ are considered as unknown numbers, simultaneousequations including four equations are necessary to calculate thesevalues. Therefore, in addition to the aforementioned valueE[X₁(t)*Y₁₁*(t)], three ensemble averages, that is, E[X₁(t)*Y₂₁*(t)],E[X₁(t)*Y₃₁*(t)] and E[X₁(t)*Y₄₁*(t)] are actually calculated.

By actually calculating individual correlation values (ensembleaverages) between the user signals and inputting as substitution to theresult of development of the aforementioned three ensemble averages,simultaneous equations where unknown numbers are H₁₁, H₂₁, H₃₁ and H₄₁are obtained. By solving the equations, it is possible to estimate withhigh precision, the reception signal coefficient vectors H₁₁, H₂₁, H₃₁and H₄₁ which are close to the actual propagation environment. In theinterference canceller of the next stage, the correlation values amonguser signals are actually calculated in the similar manner and thereception signal coefficient vector is estimated.

In the interference canceller of each stage, even when it is determinedby the interference removing unit of the preceding stage that there isno error and the replica signal has been already subtracted once, thereplica signal is again subtracted from the initial input signal vector,and hence, in order to improve accuracy of removal, parameter estimatorsPEA₁₂, . . . , PEA_(k2), . . . , PEA_(m2) are provided separately.

Particularly, in the fourth embodiment, regardless of the result ofdetermination as to the demodulation error in the extracted signal bythe error determining unit, individual correlation value (ensembleaverage) between every user is actually calculated and used. Therefore,it is possible that there is a demodulation error for any user. When thecorrelation value between a signal with an error and a signal without anerror is close to the correlation value of the actual signals(error-free signal and error-free signal), however, the reception signalcoefficient vector that is close to the actual propagation environmentcan be estimated.

As described above, according to the fourth embodiment of the presentinvention, the correlation value between user signals that has beenregarded as 0 is actually calculated, and therefore, a reception signalcoefficient vector without any error can be estimated.

Fifth Embodiment

FIG. 11 is a block diagram representing the reception system for thePDMA base station in accordance with the fifth embodiment of the presentinvention. The configuration of the reception system shown in FIG. 11 isthe same as that of the reception system in accordance with the fourthembodiment shown in FIG. 10, except for the following point.

More specifically, in addition to the configuration of the fourthembodiment shown in FIG. 10, in FIG. 11, the system is configured suchthat the error determination signal of the error determining unit ofeach user is applied to the parameter estimators of the interferenceremoving units of all the users. As a result, it becomes possible todetermine whether the correlation value between signals is to becalculated or not, dependent on the presence/absence of the demodulationerror.

More specifically, description will be given using the example of thefourth embodiment described above. Assume that it is determined thatthere is no demodulation error in the extracted signals of users 1 and 2while there is demodulation error in the extracted signals of users 3and 4, among the four users. As to the signal of the user with an error,the user signal is to be newly extracted by the interference cancellerof the next stage.

Therefore, in the fifth embodiment, only the correlation between thesignals of users 1 and 2 free of any error is used, and the correlationwith the signals of users 3 and 4 with errors is regarded as 0. Forexample, in the equation (13), among the correlation values,E[Y₃₁(t)*Y₁₁*(t)] and E[Y₄₁(t)*Y₁₁*(t)] are regarded as 0. Therefore,the equation (13) can be represented as follows.E[X ₁(t)*Y ₁₁*(t)]=H ₁₁ +H ₂₁ *E[Y ₂₁(t)*Y ₁₁*(t)]

In this equation, there are two unknown numbers, that is, H₁₁, and H₂₁.Therefore, in addition to the value E[X₁(t)*Y₁₁*(t)], also the valueE[X₁(t)*Y₂₁*(t)] is calculated. The correlation value E[Y₂₁(t)*Y₁₁*(t)]of users 1 and 2 is calculated and input to development equations ofboth E[X₁(t)*Y₁₁*(t)] and E[X₁(t)*Y₂₁*(t)], then simultaneous equationsin which unknown numbers are H₁₁ and H₂₁ are obtained. By solving thesimultaneous equations, the reception signal coefficient vectors H₁₁ andH₂₁ can be calculated with high precision.

Particularly, in the fifth embodiment, the correlation value betweenuser signals free of any error is actually calculated and utilized, andtherefore, a reception signal coefficient vector closer to the actualpropagation environment can be estimated.

Sixth Embodiment

FIG. 12 is a block diagram representing the reception system for thePDMA base station in accordance with the sixth embodiment of the presentinvention. The configuration of the reception system shown in FIG. 12 isthe same as that of the reception system in accordance with the secondembodiment shown in FIG. 6, except the following point.

More specifically, in the second embodiment shown in FIG. 6, the usersignal that is a complex signal output from the re-modulator included ineach interference removing unit IC is applied only to the parameterestimator that is included in that interference removing unit, and notapplied to the parameter estimators of interference removing units ofother users. In the sixth embodiment shown in FIG. 12, similar to thefourth embodiment shown in FIG. 10, the user signal output from there-modulator of the interference removing unit of each user is appliedto the parameter estimators of the interference removing units of allother users, in addition to the user of interest.

The reception system in accordance with the sixth embodiment shown inFIG. 12 differs from the reception system in accordance with the fourthembodiment shown in FIG. 10, in the following point.

In the configuration of the sixth embodiment shown in FIG. 12, thereplica signal of the user newly determined to be free of any error issubtracted not from the initial input signal vector X₁(t) but from theinput signal vector calculated by the operating apparatus of thecorresponding interference canceller. More specifically, subtraction ofthe replica signal is not repeated for the user that has already beendetermined to be free of any error by the interference canceling unit ofthe preceding stage, and it becomes unnecessary to add parameterestimating units PEA₁₂, . . . , PEA_(k2), PEA_(m2) as in the fourthembodiment shown in FIG. 10.

Rather, gate units GH₁₂, . . . , GH_(k2), . . . , GH_(m2) are provided,which select, dependent on presence/absence of an error at theinterference removing unit of the preceding stage, either the usersignal newly calculated by the interference removing unit of thecorresponding interference canceller or the user signal that has beenalready calculated by the interference removing unit of the precedingstage to be an object of correlation value calculation.

As described above, according to the sixth embodiment of the presentinvention, the correlation value between the user signals that has beenregarded as 0 is actually calculated, and therefore, as in the fourthembodiment, it becomes possible to estimate the reception signalcoefficient vector free of any error.

Seventh Embodiment

FIG. 13 is a block diagram representing the reception system for thePDMA base station in accordance with the seventh embodiment of thepresent invention. The configuration of the reception system shown inFIG. 13 is the same as that of the reception system in accordance withthe sixth embodiment shown in FIG. 12, except for the following point.

More specifically, in addition to the configuration of the sixthembodiment shown in FIG. 12, in the configuration of FIG. 13, the errordetermination signal of the error determining unit for each user isapplied to the parameter estimators of the interference removing unitsof all the users. As a result, dependent on presence/absence of ademodulation error, it becomes possible to determine whether thecorrelation value between signals is to be calculated or not.

Namely, in the seventh embodiment, as in the fifth embodiment, thecorrelation value between user signals that are free of any error isactually calculated and utilized, whereby it becomes possible toestimate the reception signal coefficient vector closer to the actualpropagation environment.

Eighth Embodiment

FIG. 14 is a block diagram representing the reception system for thePDMA base station in accordance with the eighth embodiment of thepresent invention. Basically, the reception system in accordance withthe eighth embodiment corresponds to the configuration of the receptionsystem in accordance with the third embodiment shown in FIG. 8, to whichthe technique described with respect to the fourth embodiment shown inFIG. 10 is applied.

More specifically, in the third embodiment shown in FIG. 8, the usersignal that is a complex signal output from the re-modulator (FIG. 9)included in each interference removing unit is applied only to theparameter estimator of the corresponding interference removing unit andnot applied to the parameter estimators of the interference removingunits of other users. In the eighth embodiment shown in FIG. 14, theuser signal output from the re-modulator of each user is applied to theparameter estimators of the interference removing units of the users ofthe next and the following stages, in addition to the correspondinguser.

More specifically, in the eighth embodiment shown in FIG. 14, it isconsidered that the initial input signal vector X₁(t) is commonly inputto respective interference removing units IC, and applied to thepositive input of adder AD and the parameter estimator PE of eachinterference calculating unit IC, as will be described later. The inputsignal vector output from the interference removing unit of thepreceding stage is applied to the adaptive array AA of the correspondinginterference removing unit (in the interference removing unit IC₁₁ ofthe first stage, the initial input signal vector X₁(t) is applied toadaptive array AA₁₁).

In the interference removing unit IC₁₁ of the first stage interferencecanceller, parameter is estimated by applying the user signal Y₁₁(t)generated by the corresponding interference removing unit to parameterestimator PE_(1k) as shown in FIG. 9, and user signals of other usersare not used.

In the interference removing unit IC₁₂ of the succeeding stage, however,in addition to the user signal Y₁₂(t) generated by the correspondinginterference removing unit, the user signal Y₁₁(t) generated by theinterference removing unit IC₁₁ of the preceding stage is also used forparameter estimation.

Similarly, the interference removing unit of each stage performsparameter estimation using, in addition to the user signal generated bythat interference removing unit, the user signal from the interferenceremoving unit preceding to that interference removing unit.

For example, the interference removing unit IC_(1m) of the lowest stageof the first stage interference canceller performs parameter estimationusing, in addition to the user signal Y_(1m)(t) generated in thatinterference removing unit, the user signals Y₁₁(t), . . . ,Y_(1(m−1))(t) generated by the interference removing units IC₁₁, . . . ,IC_(1(m−1)) of the preceding stage.

FIG. 15 is a block diagram representing a configuration of theinterference removing unit IC_(1k) of the kth stage of the first stageinterference canceller, as an example of the interference removing unitshown in FIG. 14. The interference removing unit shown in FIG. 15differs from the interference removing unit shown in FIG. 9 in thefollowing point.

More specifically, the input signal vector X_(1k)(t) output from theinterference removing unit of the preceding stage is applied only to theadaptive array AA_(1k), and the initial input signal X_(1k)(t) isapplied to the input of parameter estimator PE_(1k) and the positiveinput of adder AD_(1k). To the parameter estimator PE_(1k), the usersignal Y_(1k)(t) generated by that interference removing unit and, inaddition, user signals Y₁₁(t), . . . , Y_(1(k−1))(t) from interferenceremoving units IC₁₁, . . . , IC_(1(k−1)) of the preceding stage areapplied, and based on the correlation values among these user signals,parameter estimator PE_(1k) calculates reception signal coefficientvectors H₁₁, H₁₂, . . . , H_(1k).

The user signals Y₁₁(t), . . . , Y_(1k)(t) and the reception signalcoefficient vectors H₁₁, . . . , H_(1k) are multiplied by correspondingmultipliers MP_(1k), MP_(1k2), . . . , MP_(1kk), and the results ofmultiplication are applied to the negative inputs of adder AD_(1k)through AND gates AND_(1k1), AND_(1k2), AND_(1kk), respectively.

To the other input of AND gates AND_(1k1), AND_(1k2), . . . , AND_(1kk),error determination signals E₁₁, . . . , E_(1(k−1)) from theinterference removing units IC₁₁, . . . , IC_(1(k−1)) of the precedingstages as well as the error determination signal E_(1k) generated by theinterference removing unit of interest are input, respectively, and theAND gate that receives as an input the error determination signalindicating presence of an error is closed, so that subtraction from thereplica signal including the error from the initial input signal vectorX₁(t) is avoided.

As a result, an input signal vector X_(1(k+1))(t) not including anynoise component is output from adder AD_(1k), which is applied to theadaptive array AA_(1(k+1)) of the interference removing unit IC_(1(k+1))of the next stage.

It is understood that the interference removing units IC₂₁, IC₂₂, . . .of the interference cancellers of the second and the following stageshave the similar configuration.

In summary, in the examples shown in FIGS. 14 and 15, the receptionsignal coefficient vectors H₁₁, H₁₂, . . . , H_(1k), . . . , H_(1m) ofinterference removing units IC₁₁, . . . , IC_(1m) are calculated in thefollowing manner. First, the initial input signal vector X₁(t) is givenby the following equation.X ₁(t)=H ₁₁ Y ₁₁(t)+ . . . +H _(1k) Y _(1k)(t)+ . . . +H _(1m) Y_(1m)(t)

In the configuration of the interference canceller of the first stageshown in FIG. 14, the user signal Y_(1k)(t) can be estimated based onthe initial input signal vector X₁(t) by the interference removing unitIC of each stage. Therefore, when an ensemble average between each usersignal and the initial input signal vector X₁(t) is calculated,simultaneous equations for calculating the reception signal coefficientvectors H₁₁, H₁₂, . . . , H_(1k), . . . , H_(1m) can be obtained withthe correlation value between the users (ensemble average) calculatedactually.

Further, the operation of the interference canceller of the next stageis basically the same as the operation described with reference to FIG.8, except for the following point.

More specifically, to the gate unit GE₂₁, user signals Y₁₂(t), . . . ,Y_(1m)(t) and error determination signals E₁₂, . . . , E_(1m) areapplied from the interference removing units IC₁₂, . . . , IC_(1m) ofthe preceding stage, and when it is determined that there is an error byinterference removing unit IC₁₁, the user signals Y₁₂(t), . . . ,Y_(1m)(t) and the error determination signals E₁₂, . . . , E_(1m) areapplied to interference removing unit IC₂₁, among which the user signalsare used for parameter estimation.

Next, to the gate unit GE₂₂, user signals Y₁₃(t), . . . , Y_(1m)(t),Y₂₁(t) and error determination signals E₁₃, . . . , E_(1m), E₂₁ areapplied from interference removing units IC₁₃, . . . , IC_(1m) and IC₂₁of the preceding stage, and when it is determined that there is an errorby interference removing unit IC₁₂, the user signals Y₁₃(t), . . . ,Y_(1m)(t), Y₂₁(t) and the error determination signals E₁₃, . . . ,E_(1m), E₂₁ are applied to interference removing unit IC₂₂, among whichthe user signals are used for parameter estimation. Thereafter, similaroperation (parameter estimation) is executed by the interferenceremoving unit of each stage of the interference canceller.

As described above, the reception system in accordance with the eighthembodiment shown in FIG. 14 contemplates to calculate the receptionsignal coefficient vector of each user, additionally considering thecorrelation values among a plurality of user signals. Therefore, as inthe reception system in accordance with the fourth embodiment describedabove, by the reception system in accordance with the eighth embodiment,a reception signal coefficient vector closer to that obtained in theactual propagation environment can be estimated with high precision.

Ninth Embodiment

FIG. 16 is a block diagram representing the configuration of theinterference removing unit of the reception system for the PDMA basestation in accordance with the ninth embodiment of the presentinvention. Basically, the reception system in accordance with the ninthembodiment has the same overall configuration as the reception systemshown in FIG. 14 except for the configuration of the interferenceremoving unit, and it corresponds to the configuration of the receptionsystem in accordance with the third embodiment shown in FIG. 8 to whichthe technique described with reference to the fifth embodiment shown inFIG. 11 is applied. The interference removing unit shown in FIG. 16 isthe same as the interference removing unit in accordance with the eighthembodiment shown in FIG. 15 except for the following point.

More specifically, in addition to the configuration of the interferenceremoving unit in accordance with the eighth embodiment shown in FIG. 15,in the ninth embodiment shown in FIG. 16, the error determinationsignals (for example, E₁₁, . . . , E_(1(k−1))) of the error determiningunits of the interference removing units of the preceding stage areapplied to the parameter estimating unit of the interference removingunit of the next stage.

In the reception system in accordance with the ninth embodiment shown inFIG. 16, whether calculation of the correlation value between thesignals is to be performed or not is determined dependent on thepresence/absence of a demodulation error. Particularly, in the receptionsystem in accordance with the ninth embodiment, the correlation value iscalculated only between the user signals that are free of any error tobe used for calculating the reception signal coefficient vector. Thus,as in the reception system in accordance with the fifth embodimentdescribed above, it becomes possible to estimate the reception signalcoefficient vector closer to the one obtained in the actual propagationenvironment with high precision.

Tenth Embodiment

The embodiments shown in FIGS. 3 to 16 are directed to the receptionsystem for PDMA base station. Recently, CDMA communication method hasbeen proposed and comes to be practically used, in addition to the PDMAcommunication method.

In the CDMA communication method, on the transmitting side, thetransmitted digital data has it symbol multiplied by a prescribedspreading code so that it is transmitted as a signal with extremely highfrequency, and on the receiving side, the received signal is inversespread using the spreading code, so as to demodulate the data.

Here, when a plurality of different spreading codes not having anycorrelation with each other are used, it becomes possible to surelyseparate and extract only the signals of a desired user by performinginverse spreading with the spreading code that corresponds totransmission, even when a plurality of data signals of the samefrequency are spread and transmitted. Therefore, use of the CDMAcommunication method enables further increase of communication capacity.Such CDMA communication method has been already practically used andwell known in the field of art, and therefore, detailed description isnot given here.

The following embodiment is the application of the radio receptionsystem in accordance with the present invention to the CDMAcommunication method.

FIG. 17 is a block diagram representing the reception system for theCDMA base station in accordance with the tenth embodiment of the presentinvention. FIGS. 18 and 19 are specific block diagrams of theinterference removing unit and the operating apparatus shown in FIG. 17,respectively.

The CDMA reception system in accordance with the tenth embodiment shownin FIGS. 17 to 19 is the same as the PDMA reception system in accordancewith the first embodiment shown in FIGS. 3 to 5, except for thefollowing points.

More specifically, the configuration of the interference removing unitIC of the reception system in accordance with the first embodiment shownin FIG. 3 is changed from that of the first embodiment shown in FIG. 4to the configuration in accordance with the tenth embodiment shown inFIG. 18. In the interference removing unit (as an example, interferenceremoving unit IC_(k1)′) shown in FIG. 18, in a preceding stage of theadaptive array and a parameter estimator, there is provided an inversespreader IS_(k1) for inverse spreading the signals that have beentransmitted in accordance with the CDMA communication method andreceived by antennas 3 to 6. Reception signals that have been inversespread user by user by the inverse spreader at respective interferenceremoving units are applied to the corresponding adaptive arrays and aparameter estimators, respective user signals are extracted through thesame operation as in the first embodiment described above, and theextracted signals are applied to the operating apparatus of theinterference canceller of the succeeding stage.

The operating apparatus 101 a of the first stage interference cancellershown in FIG. 19 is the same as the operating apparatus 101′ shown inFIG. 5, except that spreaders S₁₁, . . . , S_((k−1)1), S_(k1),S_((k+1)1), S_(m1), spreading outputs of multipliers MP₁, . . . ,MP_(k−1), MP_(k), MP_(k+1), . . . , MP_(m) are provided.

More specifically, in order to perform subtraction from the input signalvector X₁(t) that has been spread in accordance with the CDMAcommunication method, the output of each multiplier is spread again bythe corresponding spreading code.

Then, the output of each spreader, that is, the output of operatingapparatus 101 a is again inverse spread by the inverse spreader of thecorresponding interference removing unit of the succeeding stage, andapplied to the adaptive array and a parameter estimator.

The operating apparatus 102 a of the second stage interference cancellerhas the same configuration as the operating apparatus 101 a shown inFIG. 19. Other operations are the same as those of the first embodimentshown in FIGS. 3 to 5.

Eleventh Embodiment

FIG. 20 is a block diagram representing the reception system for theCDMA base station in accordance with the eleventh embodiment of thepresent invention. The eleventh embodiment shown in FIG. 20 is the sameas the third embodiment shown in FIG. 8 except for the following point.Namely, for the interference removing unit of each stage, an inversespreader for inverse spreading the input signal vector that has beentransmitted in accordance with the CDMA communication method is provided(in the interference removing unit IC_(1k)′ of FIG. 9, inverse spreaderIS_(1k)), in the preceding stage of the corresponding adaptive array anda parameter estimator. The input signal vectors inverse spread user byuser by respective inverse spreaders are applied to the correspondingadaptive arrays and a parameter estimators, and respective user signalsare extracted by the same operation as the third embodiment describedabove. The output of the multiplexer in each interference removing unitis again spread by a spreader (in FIG. 9, spreader S_(1k)), so as toperform subtraction from the corresponding input signal vector that hasbeen spread by the CDMA method. Other operations are the same as thoseof the third embodiment shown in FIG. 8, and therefore, descriptionthereof will not be repeated.

Though examples in which the CDMA communication method is applied to thefirst embodiment shown in FIGS. 3 to 5 and to the third embodiment shownin FIGS. 8 and 9 have been described as the tenth and eleventhembodiments, it is needless to say that the CDMA communication methodcan similarly be applied to the reception systems disclosed as otherembodiments, though not shown.

FIG. 21 is a block diagram representing an example of the adaptive array17 used in the reception system in each of the above describedembodiments.

Referring to FIG. 21, each adaptive array is provided with input ports181 to 184, to which input ports input signals from four antennas 3 to 6that have been A/D converted by A/D converter 8 are input, respectively.The input signals are applied to a weight vector calculator 176 andmultipliers 171 to 174.

Weight vector calculator 176 calculates weight vectors w1 to w4 so thata desired user signal is extracted, using the input signals from inputports 181 to 184 and a training signal corresponding to a specific usersignal stored in advance in a memory 177 or an output of adder 175.

Multipliers 171 to 174 multiply the input signals of input ports 181 to184 by the weight vectors w1 to w4, respectively, and provide theresults to adder 175. Adder 175 adds respective output signals frommultipliers 171 to 174, applies the resulting desired user signal toweight vector calculator 176 and outputs from an output port.

The first to eleventh embodiments described above are configured suchthat data re-modulated by a re-modulator is applied to the operatingapparatus or the like. The output of the adaptive array and there-modulated data can be essentially regarded as the data of the samecontents, and therefore, similar effects can be attained even when anoutput data of adaptive array is input to the operating apparatus or thelike.

In each of the above described embodiments, the reception system isimplemented by a hardware configuration in which plural stages ofinterference cancellers are connected. These reception systems as awhole may be implemented by a software, using a digital signal processor(DSP).

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

As described above, according to the present invention, an interferinguser signal component extracted by the signal extracting meanscorresponding to the user is removed from the input signal vector by theinterference removing means, whereby the desired user signal componentcan be extracted with the interfering component much suppressed, andhence communication quality in a radio communication system such asmobile communication system can be improved.

Further, a user signal which is determined to have a demodulation erroris excluded from the subtraction of the interfering wave component, andtherefore, noise is not included in the output signal from theinterference canceller.

Further, when estimating the reception signal coefficient vector, acorrelation value between the signal component of a user of interest andthe signal component of other user is actually calculated, andestimation is performed based on the result. Therefore, a receptionsignal coefficient vector closer to the one obtained in the actualpropagation environment can be obtained, and thus it becomes possible toremove the interfering wave with higher precision.

INDUSTRIAL APPLICABILITY

As described above, the radio reception system in accordance with thepresent invention is applicable to improve communication quality byremoving unnecessary user signal among signals received by a mobileterminal apparatus, in a base station of a mobile communication systemsuch as PDMA or CDMA.

1. A radio reception system capable of receiving signals from aplurality of transmitters using a plurality of antennas, comprising: asignal processing unit performing a prescribed signal processing on thesignals received by said plurality of antennas; a plurality of firstsignal extracting units extracting signal components corresponding tosaid plurality of transmitters, respectively, based on a signal outputfrom said signal processing unit; a plurality of first estimating unitsestimating parameter information related to relation between the signalcomponents extracted by said first signal extracting units and thereceived signal output from said signal processing units; a plurality offirst error determining units determining whether the signal componentscorresponding to the plurality of transmitters extracted by said firstsignal extracting units include a demodulation error or not,respectively; and a first operating unit subtracting, from the signaloutput from said signal processing unit, said extracted signal componentdetermined by said first error determining unit not to include anydemodulation error, in consideration of corresponding said parameterinformation.
 2. The radio reception system according to claim 1, furthercomprising: a plurality of second signal extracting units extracting,based on the signal output from said first operating unit, signalcomponents corresponding to transmitters determined by said first errordetermining units to include a demodulation error, respectively; aplurality of second estimating units for estimating parameterinformation related to relation between the signal components extractedby said second signal extracting units and the signal output from saidfirst operating unit; and a plurality of second error determining unitsdetermining whether the signal components extracted by said secondsignal extracting units include a demodulation error or not,respectively.
 3. The radio reception system according to claim 2,further comprising: a second operating unit subtracting, from the signaloutput from said signal processing unit, the signal component extractedby said first and second signal extracting units determined by saidfirst and second error determining units not to include any demodulationerror, in consideration of corresponding said parameter information. 4.The radio reception system according to claim 2, further comprising athird operating unit subtracting, from the signal output from said firstoperating unit, the signal component extracted by said second signalextracting unit determined by said second error determining unit not toinclude any demodulation error, in consideration of corresponding saidparameter information.
 5. A radio reception system capable of receivingsignals from a plurality of transmitters using a plurality of antennas,comprising: a signal processing unit performing a prescribed signalprocessing on the signals received by said plurality of antennas; aplurality of first signal extracting units extracting signal componentscorresponding to said plurality of transmitters, respectively, based ona signal output from said signal processing unit; a plurality of firstestimating units estimating parameter information related to relationbetween the signal components extracted by said first signal extractingunits and the signal output from said signal processing unit based on acorrelation value between signal component of the correspondingtransmitter and signal component of another transmitter; a plurality offirst error determining units determining whether the signal componentscorresponding to the plurality of transmitters extracted by said firstsignal extracting units include a demodulation error or not,respectively; and a first operating unit subtracting, from the signaloutput from said signal processing unit, said extracted signal componentdetermined by said first error determining unit not to include anydemodulation error, in consideration of corresponding said parameterinformation.
 6. The radio reception system according to claim 5, furthercomprising a plurality of second signal extracting units extracting,based on the signal output from said first operating unit, signalcomponents corresponding to transmitters determined by said first errordetermining units to include a demodulation error, respectively; aplurality of second estimating units estimating parameter informationrelated to relation between the signal components extracted by saidsecond signal extracting units and the signal output from said firstoperating unit based on a correlation value between signal component ofthe corresponding transmitter and signal component of anothertransmitter; and a plurality of second error determining units fordetermining whether the signal components extracted by said secondsignal extracting units include a demodulation error or not,respectively.
 7. The radio reception system according to claim 6,further comprising a second operating unit subtracting, from the signaloutput from said signal processing unit, the signal component extractedby said first and second signal extracting units determined by saidfirst and second error determining units not to include any demodulationerror, in consideration of corresponding said parameter information. 8.The radio reception system according to claim 6, further comprising athird operating unit subtracting, from the signal output from said firstoperating unit, the signal component extracted by said second signalextracting unit determined by said second error determining unit not toinclude any demodulation error, in consideration of corresponding saidparameter information.
 9. The radio reception system according to any ofclaims 5 to 8, wherein said plurality of first estimating units estimatesaid parameter information by calculating said correlation value,independent from result of determination by said plurality of firsterror determination units.
 10. The radio reception system according toany of claims 5 to 8, wherein said plurality of first estimating unitsestimate said parameter information by calculating said correlationvalue using signal components of the users determined not to include anydemodulation error, based on the result of determination by saidplurality of first error determining units.
 11. The radio receptionsystem according to any of claims 6 to 8, wherein said plurality ofsecond estimating units estimate said parameter information bycalculating said correlation value, independent from result ofdetermination by said plurality of second error determination units. 12.The radio reception system according to any of claims 6 to 8, whereinsaid plurality of second estimating units estimate said parameterinformation by calculating said correlation value using signalcomponents of the transmitter determined not to include any demodulationerror, based on the result of determination by said plurality of seconderror determining units.
 13. A radio reception system capable ofreceiving signals from a plurality of transmitters using a plurality ofantennas, comprising: a signal processing unit for performing aprescribed signal processing on the signals received by said pluralityof antennas; and a first stage of interference cancellers, including aplurality of stages of interference removing units corresponding to saidplurality of transmitters; wherein each stage of said interferenceremoving units includes a first signal extracting unit extracting signalcomponent corresponding to a specific transmitter, different stage bystage, among said plurality of transmitters based on an input signal, afirst estimating unit estimating parameter information related torelation between the signal component extracted by said first signalextracting unit and the signal input to said first signal extractingunit, a first operating unit for removing the signal componentcorresponding to said specific transmitter, from the signal input tosaid first signal extracting unit in consideration of said parameterinformation, and a first error determining unit determining whether thesignal component corresponding to said specific transmitter includes ademodulation error or not, and when determined to include thedemodulation error, disabling removal of the signal componentcorresponding to said specific transmitter by said first operating unit;and said plurality of stages of interference removing units areconnected such that the signal output from said signal processing unitis input to inputs of said first operating unit and said first signalextracting unit of the first stage of said interference removing units,and an output of said operating unit of a former stage interferenceremoving unit of adjacent two interference removing units is applied toinputs of said signal extracting unit and said operating unit of alatter stage interference removing unit.
 14. The radio reception systemaccording to claim 13, further comprising a next stage of interferencecancellers receiving an output of said operating unit of a last stageinterference removing unit of said first stage of interferencecancellers; wherein said next stage interference canceller includes aplurality of stages of interference removing units corresponding to saidplurality of transmitters; each stage of said interference removingunits includes a second signal extracting unit extracting and outputtingsignal component corresponding to a specific transmitter, differentstage by stage, among said plurality of transmitters, based on an inputsignal, a second estimating unit estimating parameter informationrelated to relation between the signal component extracted by saidsecond signal extracting unit and the signal input to said second signalextracting unit, a second operating unit removing the signal componentcorresponding to said specific transmitter from the signals input tosaid second signal extracting unit, in consideration of said parameterinformation, and a second error determining unit determining whether thesignal component corresponding to said specific transmitter includes ademodulation error or not and, when determined to include an error,disabling removal of the signal component corresponding to said specifictransmitter by said second operating unit; the interference removingunit of said next stage interference canceller corresponding to atransmitter determined not to include any demodulation error by theinterference canceller of said first stage provides an output of theinterference removing unit of the preceding stage as it is to theinterference removing unit of the succeeding stage; and in theinterference removing unit of said next stage interference cancellercorresponding to the transmitter determined to include a demodulationerror by said first stage interference canceller, an output of theinterference removing unit of the preceding stage is applied to inputsof said signal extracting unit and said operating unit, and an output ofsaid operating unit is output to the interference removing unit of thesucceeding stage.
 15. A radio reception system capable of receivingsignals from a plurality of transmitters using a plurality of antennas,comprising: a signal processing unit performing a prescribed signalprocessing on the signals received by said plurality of antennas; and afirst stage of interference cancellers; said first stage of interferencecanceller includes a plurality of stages of interference removing unitscorresponding to said plurality of transmitters; each stage of saidinterference removing units includes a first signal extracting unitextracting and outputting signal component corresponding to a specifictransmitter, different stage by stage, among said plurality oftransmitters, based on an input signal, a first estimating unitestimating, based on a correlation value between signal component ofsaid specific transmitter and signal component of another transmitter,parameter information related to relation between the signal componentextracted by said first signal extracting unit and the signal outputfrom said signal processing unit, a first error determining unitdetermining whether the signal component corresponding to said specifictransmitter includes a demodulation error or not, and a first operatingunit removing the signal component corresponding to a transmitterdetermined not to include a demodulation error from the signal outputfrom said signal processing unit, in consideration of said parameterinformation; and said plurality of stages of interference removing unitsare connected such that the signal output from said signal processingunit is input to inputs of said first operating unit and said firstsignal extracting unit of the first stage of said interference removingunits, and an output of said operating unit of a former interferenceremoving unit of adjacent two interference removing units is applied toan input of said signal extracting unit of a latter stage interferenceremoving unit.
 16. The radio reception system according to claim 15,further comprising a next stage of interference cancellers receiving anoutput of said operating unit of the interference removing unit of thelast stage of said first stage of interference cancellers; wherein saidnext stage interference canceller includes a plurality of stages ofinterference removing units corresponding to said plurality oftransmitters; each stage of said interference removing unit includes asecond signal extracting unit extracting and outputting signal componentcorresponding to a specific transmitter, different stage by stage, amongsaid plurality of transmitters based on an input signal, a secondestimating unit estimating, based on a correlation value between signalcomponent of said specific transmitter and signal component of anothertransmitter, parameter information related to relation between thesignal component extracted by said second signal extracting unit and thesignal output from said signal processing unit, a second errordetermining unit determining whether or not the signal componentcorresponding to said specific transmitter includes a demodulationerror, and second operating unit removing the signal componentcorresponding to the transmitter determined not to include anydemodulation error from the signal output from said signal processingunit, in consideration of said second parameter information; theinterference removing unit of said next stage interference cancellercorresponding to the transmitter determined not to include anydemodulation error by said first stage interference canceller outputs anoutput of the interference removing unit of the preceding stage as it isto an interference removing unit of the succeeding stage; and in theinterference removing unit of said next stage interference cancellercorresponding to the transmitter determined to include a demodulationerror by said first stage interference canceller, an output of theinterference removing unit of the preceding stage is applied to an inputof said signal extracting unit, and an output of said operating unit isoutput to the interference removing unit of the succeeding stage. 17.The radio reception system according to claim 15, wherein said firstestimating unit calculates correlation value between the signalcomponent of said specific transmitter and signal component of anothertransmitter independent from result of determination by said first errordetermining unit, and estimates said parameter information based on thecalculated correlation value.
 18. The radio reception system accordingto claim 15, wherein said first estimating unit calculate thecorrelation value using only the signal components of the transmittersdetermined not to include any demodulation error based on the result ofdetermination by said first error determining unit, and estimates saidparameter information based on the calculated correlation value.
 19. Theradio reception system according to claim 1, 5, 13 or 15, wherein saidsignal extracting unit is an adaptive array spatially separating andextracting signal component corresponding to a specific transmitter. 20.The radio reception system according to claim 1, 5, 13 or 15, whereinsaid signal extracting unit includes an adaptive array spatiallyseparating and extracting signal component corresponding to a specifictransmitter, a demodulator demodulating an output of said adaptivearray, and a re-modulator re-modulating an output of said demodulator.21. The radio reception system according to claim 1, 5, 13 or 15,wherein the signals from said plurality of transmitters are signalstransmitted in accordance with PDMA communication method.
 22. The radioreception system according to claim 1, 5, 13 or 15, wherein the signalsfrom said plurality of transmitters are signals transmitted inaccordance with CDMA communication method.
 23. The radio receptionsystem according to claim 22, wherein the signals transmitted inaccordance with said CDMA communication method are spread bypredetermined spreading codes in advance on a transmitting side, saidsystem further comprising an inverse spreading unit inverse spreadingsignals output from said signal processing unit by correspondingspreading codes in accordance with CDMA communication method andapplying the results to said signal extracting unit.
 24. The radioreception system according to claim 16, wherein said second estimatingunit calculates the correlation value between the signal component ofsaid specific transmitter and signal component of another transmitterindependent from result of determination by said second errordetermining unit, and estimates said parameter information based on thecalculated correlation value.
 25. The radio reception system accordingto claim 16, wherein said second estimating unit calculates thecorrelation value using only the signal component of the transmittersdetermined not to include any demodulation error based on the result ofdetermination by said second error determining unit, and estimates saidparameter information based on the calculated correlation value.